dist: obsolete support for lzma (superseded by xz and lzip)

dist: obsolete support for lzma (superseded by xz and lzip)

The lzma utilities are today superseded by the xz utilities; in
fact, the official site at <http://tukaani.org/lzma/> reads:

  ``LZMA Utils are legacy data compression software with high
    compression ratio.  LZMA Utils are no longer developed, ...
    Users of LZMA Utils should move to XZ Utils.''

and the existing automake manual (as of 1.11.2) already says:

  ``dist-xz
    Generate an 'xz' tar archive of the distribution. xz archives
    are frequently smaller than bzip2-compressed archives. The 'xz'
    format will soon (early 2009) displace the 'lzma' format''

Also, the `dist-lzma' target still suffers of never-solved bugs,
due to the too-high compression ratio its uses by default, which
might cause an unacceptable memory consumption when one tries to
compress or, worse, decompress the created tarballs; see also:

  <http://lists.gnu.org/archive/html/automake/2011-12/msg00025.html>
  <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=9658>

* NEWS: Update.
* doc/automake.texi (Dist, Options): State that `dist-lzma' will
go away in the next major automake version.
* lib/Automake/Options.pm (_process_option_list): Deprecate
`dist-lzma'.
* tests/lzma.test: Update.