Update XZ Utils to 5.0.3 (in deps)

TODO

Index: TODO
===================================================================
--- TODO	(revision 50504)
+++ TODO	(working copy)
@@ -18,16 +18,21 @@
 
     XZ Utils compress some files significantly worse than LZMA Utils.
     This is due to faster compression presets used by XZ Utils, and
-    can be worked around by using "xz --extreme". However, the presets
-    need some tweaking and maybe this issue can be minimized without
-    making the typical case too much slower.
+    can often be worked around by using "xz --extreme". With some files
+    --extreme isn't enough though: it's most likely with files that
+    compress extremely well, so going from compression ratio of 0.003
+    to 0.004 means big relative increase in the compressed file size.
 
     xz doesn't quote unprintable characters when it displays file names
     given on the command line.
 
     tuklib_exit() doesn't block signals => EINTR is possible.
 
+    SIGTSTP is not handled. If xz is stopped, the estimated remaining
+    time and calculated (de)compression speed won't make sense in the
+    progress indicator (xz --verbose).
 
+
 Missing features
 ----------------
 
@@ -41,11 +46,13 @@
     Buffer-to-buffer coding could use less RAM (especially when
     decompressing LZMA1 or LZMA2).
 
-    I/O library is not implemented. It will possibly be named libzzf.
+    I/O library is not implemented (similar to gzopen() in zlib).
+    It will be a separate library that supports uncompressed, .gz,
+    .bz2, .lzma, and .xz files.
 
     lzma_strerror() to convert lzma_ret to human readable form?
     This is tricky, because the same error codes are used with
-    slightly different meanings.
+    slightly different meanings, and this cannot be fixed anymore.
 
 
 Documentation