multilib: move to contrib

multilib: move to contrib

This follows up on commit v1.11-665-gc5df21e of 2012-01-17,
"multilib: deprecate, will be moved to contrib".  See also:
<http://lists.gnu.org/archive/html/automake-patches/2012-01/msg00109.html>

* NEWS: Update.
* automake.in ($seen_multilib): Remove.
(scan_autoconf_traces): Don't trace 'AM_ENABLE_MULTILIB', and don't
handle it anymore.
(handle_multilib): Remove.
(generate_makefile): Don't call it anymore.
* doc/automake.texi: Remove documentation about multilib support,
related macros, and helper files.
* m4/multi.m4: Delete.
* m4/Makefile.am (dist_automake_ac_DATA): Remove it.
* lib/am/multilib.am: Delete.
* lib/am/Makefile.am (dist_am_DATA): Remove it.
* contrib/multilib/multilib.am: New file, adapted from extracts of
a Makefile.in generated with automake multilib support.  We did
this instead of moving and editing 'lib/am/multilib.am' because it
allows us to license this file with a liberal license that will
permit users to copy-and-paste it in non-GPLed Makefile.am files
too).
* lib/symlink-tree, lib/config-ml.in: Move ...
* contrib/multilib: ... in here.
* lib/Makefile.am (dist_script_DATA, dist_pkgvdata_DATA): Update.
* contrib/multilib/README: New file.
* contrib/Makefile.am (EXTRA_DIST): Add the files created or moved
in 'contrib/multlib'.
* tests/multilib.test: Update and enhance a little.
* tests/help-multilib.test: Likewise.