dist: ordering of files in DIST_COMMON is deterministic now

dist: ordering of files in DIST_COMMON is deterministic now

It had likely stopped being deterministic due to the new perl behavior
of having non-deterministic order of numerating hash keys:
<http://search.cpan.org/dist/perl-5.18.0/pod/perldelta.pod#Hash_randomization>
<http://onionstand.blogspot.ie/2012/12/are-you-relying-on-hash-keys-being.html>
See also similar commit v1.14-19-g52e6404, albeit in this case the issue
is likely coming from autom4te/autoconf, not from automake itself.

Fixes automake bug http://debbugs.gnu.org/17908

* bin/automake.in (handle_dist): Sort @dist_common.
(print_autodist_files): Swap invocations of 'sort' and 'uniq', for
consistency with the new code in 'handle_dist' and to get rid of a
minor hack.
* NEWS: Update.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>