Merge branch 'master' of http://git.tukaani.org/xz into experimental

Merge branch 'master' of git.tukaani.org/xz into experimental

Sync with upstream.  The memory requirements for the new presets
are not documented, so let's not impose them on sid users yet.

* 'master' of http://git.tukaani.org/xz:
  Adjust memory limits in test_compress.sh
  xz: Make -vv show also decompressor memory usage.
  Tweak the compression presets -0 .. -5.
  liblzma: Adjust default depth calculation for HC3 and HC4.
  xz: Make --help two lines shorter.
  xz: Make setting a preset override a custom filter chain.
  xz: Always warn if adjusting dictionary size due to memlimit.