Modify bsdiff 4.3 to goobsdiff, which is appropriate for use as the Mac binary differ/patcher

chrome/installer/mac/third_party/bsdiff/README.chromium

 Name: BSDiff
 URL: http://www.daemonology.net/bsdiff/
 Source URL: http://www.daemonology.net/bsdiff/bsdiff-4.3.tar.gz
 Version: 4.3
 License: BSD
 License File: LICENSE
 
 Description:
 Binary diff/patch utility. There are other copies of BSDiff in the Chromium
 repository, but they're all different. The other copies are based on Mozilla's
-fork of BSDiff, which serves a different set of needs.
+fork of BSDiff, which serves a different set of needs. Relative to upstream
+BSDiff, Mozilla's version removes all compression, adds a CRC-32 check of the
+original file, replaces the custom off_t encoding with signed 32-bit
+big-endian integers, and contains a total reorganization of the code. The
+version in this directory contains no Mozilla code and builds directly on the
+upstream version. It retains and enhances the compression, uses SHA1 to check
+both the original file and the patched file, uses a different off_t encoding
+more compatible with the original, and involves minimal changes to the
+original code.
+
+Theoretically, a hash of the original file should be enough to guarantee data
+integrity, but in the event of algorithmic or programming bugs or other
+unexpected conditions, a hash of the patched file provides a better guarantee.
+This implementation now checks the integrity of both the original and the
+patched files. SHA1, rather than CRC-32, is used to minimize the likelihood
+that an original file that has been intentionally tampered with will produce
+an altered patched file without being detected.
 
 Local Modifications:
- - Added LICENSE file by copying the license block from bsdiff.c and bspatch.c.
+ - Added LICENSE file by copying the license block from bsdiff.c and
+   bspatch.c.
+ - The following modifications are relative to the original unpatched version,
+   checked in to the Chromium repository at r49280.
+ - Created goobsdiff.gyp for GYP build system integration.
+ - Renamed bsdiff.c to goobsdiff.c and bspatch.c to goobspatch.c.
+ - Added #include <sys/types.h> to goobspatch.c so that it compiles. (Oops!)
+ - Changed the magic number in the header from BSDIFF40 to BSDIFF4G.
+ - Expanded the header to include SHA1 hashes of the original and new files,
+   and added hash checks to the patcher.
+ - Expanded the header to include the lengths of the control, diff, and extra
+   blocks in the patch file, and added patch file length validation to the
+   patcher.
+ - Replaced custom off_t encoding with signed 64-bit little-endian integers.
+ - The control, diff, and extra blocks can be compressed with bzip2 or gzip,
+   or left uncompressed, independently of one another, depending on which is
+   smallest. This often results in a net reduction in patch size of about 3%.
+ - Error messages in the patcher are slightly more descriptive.
+ - The patcher treats a few more unexpected read cases as errors than it did
+   previously. This will theoretically cause it to exit with an error instead
+   of sitting in a busy loop or crashing when certain malformatted patch files
+   are provided.