Add an unpatched version of xz, XZ Utils, to /trunk/deps/third_party

xz/README

+
+XZ Utils
+========
+
+    0. Overview
+    1. Documentation
+       1.1. Overall documentation
+       1.2. Documentation for command line tools
+       1.3. Documentation for liblzma
+    2. Version numbering
+    3. Reporting bugs
+    4. Other implementations of the .xz format
+    5. Contact information
+
+
+0. Overview
+-----------
+
+    XZ Utils provide a general-purpose data compression library and
+    command line tools. The native file format is the .xz format, but
+    also the legacy .lzma format is supported. The .xz format supports
+    multiple compression algorithms, which are called "filters" in
+    context of XZ Utils. The primary filter is currently LZMA2. With
+    typical files, XZ Utils create about 30 % smaller files than gzip.
+
+    To ease adapting support for the .xz format into existing applications
+    and scripts, the API of liblzma is somewhat similar to the API of the
+    popular zlib library. For the same reason, the command line tool xz
+    has similar command line syntax than that of gzip.
+
+    When aiming for the highest compression ratio, LZMA2 encoder uses
+    a lot of CPU time and may use, depending on the settings, even
+    hundreds of megabytes of RAM. However, in fast modes, LZMA2 encoder
+    competes with bzip2 in compression speed, RAM usage, and compression
+    ratio.
+
+    LZMA2 is reasonably fast to decompress. It is a little slower than
+    gzip, but a lot faster than bzip2. Being fast to decompress means
+    that the .xz format is especially nice when the same file will be
+    decompressed very many times (usually on different computers), which
+    is the case e.g. when distributing software packages. In such
+    situations, it's not too bad if the compression takes some time,
+    since that needs to be done only once to benefit many people.
+
+    With some file types, combining (or "chaining") LZMA2 with an
+    additional filter can improve compression ratio. A filter chain may
+    contain up to four filters, although usually only one two is used.
+    For example, putting a BCJ (Branch/Call/Jump) filter before LZMA2
+    in the filter chain can improve compression ratio of executable files.
+
+    Since the .xz format allows adding new filter IDs, it is possible that
+    some day there will be a filter that is, for example, much faster to
+    compress than LZMA2 (but probably with worse compression ratio).
+    Similarly, it is possible that some day there is a filter that will
+    compress better than LZMA2.
+
+    XZ Utils doesn't support multithreaded compression or decompression
+    yet. It has been planned though and taken into account when designing
+    the .xz file format.
+
+
+1. Documentation
+----------------
+
+1.1. Overall documentation
+
+    README              This file
+
+    INSTALL.generic     Generic install instructions for those not familiar
+                        with packages using GNU Autotools
+    INSTALL             Installation instructions specific to XZ Utils
+    PACKAGERS           Information to packagers of XZ Utils
+
+    COPYING             XZ Utils copyright and license information
+    COPYING.GPLv2       GNU General Public License version 2
+    COPYING.GPLv3       GNU General Public License version 3
+    COPYING.LGPLv2.1    GNU Lesser General Public License version 2.1
+
+    AUTHORS             The main authors of XZ Utils
+    THANKS              Incomplete list of people who have helped making
+                        this software
+    NEWS                User-visible changes between XZ Utils releases
+    ChangeLog           Detailed list of changes (commit log)
+    TODO                Known bugs and some sort of to-do list
+
+    Note that only some of the above files are included in binary
+    packages.
+
+
+1.2. Documentation for command line tools
+
+    The command line tools are documented as man pages. In source code
+    releases (and possibly also in some binary packages), the man pages
+    are also provided in plain text (ASCII only) and PDF formats in the
+    directory "doc/man" to make the man pages more accessible to those
+    whose operating system doesn't provide an easy way to view man pages.
+
+
+1.3. Documentation for liblzma
+
+    The liblzma API headers include short docs about each function
+    and data type as Doxygen tags. These docs should be quite OK as
+    a quick reference.
+
+    I have planned to write a bunch of very well documented example
+    programs, which (due to comments) should work as a tutorial to
+    various features of liblzma. No such example programs have been
+    written yet.
+
+    For now, if you have never used liblzma, libbzip2, or zlib, I
+    recommend learning *basics* of zlib API. Once you know that, it
+    should be easier to learn liblzma.
+
+        http://zlib.net/manual.html
+        http://zlib.net/zlib_how.html
+
+
+2. Version numbering
+--------------------
+
+    The version number format of XZ Utils is X.Y.ZS:
+
+      - X is the major version. When this is incremented, the library
+        API and ABI break.
+
+      - Y is the minor version. It is incremented when new features are
+        added without breaking existing API or ABI. Even Y indicates
+        stable release and odd Y indicates unstable (alpha or beta
+        version).
+
+      - Z is the revision. This has different meaning for stable and
+        unstable releases:
+          * Stable: Z is incremented when bugs get fixed without adding
+            any new features.
+          * Unstable: Z is just a counter. API or ABI of features added
+            in earlier unstable releases having the same X.Y may break.
+
+      - S indicates stability of the release. It is missing from the
+        stable releases where Y is an even number. When Y is odd, S
+        is either "alpha" or "beta" to make it very clear that such
+        versions are not stable releases. The same X.Y.Z combination is
+        not used for more than one stability level i.e. after X.Y.Zalpha,
+        the next version can be X.Y.(Z+1)beta but not X.Y.Zbeta.
+
+
+3. Reporting bugs
+-----------------
+
+    Naturally it is easiest for me if you already know what causes the
+    unexpected behavior. Even better if you have a patch to propose.
+    However, quite often the reason for unexpected behavior is unknown,
+    so here are a few things to do before sending a bug report:
+
+      1. Try to create a small example how to reproduce the issue.
+
+      2. Compile XZ Utils with debugging code using configure switches
+         --enable-debug and, if possible, --disable-shared. If you are
+         using GCC, use CFLAGS='-O0 -ggdb3'. Don't strip the resulting
+         binaries.
+
+      3. Turn on core dumps. The exact command depends on your shell;
+         for example in GNU bash it is done with "ulimit -c unlimited",
+         and in tcsh with "limit coredumpsize unlimited".
+
+      4. Try to reproduce the suspected bug. If you get "assertion failed"
+         message, be sure to include the complete message in your bug
+         report. If the application leaves a coredump, get a backtrace
+         using gdb:
+           $ gdb /path/to/app-binary   # Load the app to the debugger.
+           (gdb) core core   # Open the coredump.
+           (gdb) bt   # Print the backtrace. Copy & paste to bug report.
+           (gdb) quit   # Quit gdb.
+
+    Report your bug via email or IRC (see Contact information below).
+    Don't send core dump files or any executables. If you have a small
+    example file(s) (total size less than 256 KiB), please include
+    it/them as an attachment. If you have bigger test files, put them
+    online somewhere and include an URL to the file(s) in the bug report.
+
+    Always include the exact version number of XZ Utils in the bug report.
+    If you are using a snapshot from the git repository, use "git describe"
+    to get the exact snapshot version. If you are using XZ Utils shipped
+    in an operating system distribution, mention the distribution name,
+    distribution version, and exact xz package version; if you cannot
+    repeat the bug with the code compiled from unpatched source code,
+    you probably need to report a bug to your distribution's bug tracking
+    system.
+
+
+4. Other implementations of the .xz format
+------------------------------------------
+
+    7-Zip and the p7zip port of 7-Zip support the .xz format starting
+    from the version 9.00alpha.
+
+        http://7-zip.org/
+        http://p7zip.sourceforge.net/
+
+    XZ Embedded is a limited implementation written for use in the Linux
+    kernel, but it is also suitable for other embedded use.
+
+        http://tukaani.org/xz/embedded.html
+
+
+5. Contact information
+----------------------
+
+    If you have questions, bug reports, patches etc. related to XZ Utils,
+    contact Lasse Collin <lasse.collin@tukaani.org> (in Finnish or English).
+    tukaani.org uses greylisting to reduce spam, thus when you send your
+    first email, it may get delayed by a few hours. In addition to that,
+    I'm sometimes slow at replying. If you haven't got a reply within two
+    weeks, assume that your email has got lost and resend it or use IRC.
+
+    You can find me also from #tukaani on Freenode; my nick is Larhzu.
+    The channel tends to be pretty quiet, so just ask your question and
+    someone may wake up.
+