Merge branch 'am-prog-mkdir-p-remove'

Merge branch 'am-prog-mkdir-p-remove'

Finally backporting the AM_PROG_MKDIR_P removal that has already taken
place in Automake-NG.  We can safely do this since the latest Gettext
release (1.18.2) has removed all uses of AM_PROG_MKDIR_P, replacing
them with uses of AC_PROG_MKDIR_P instead.

References:
<http://lists.gnu.org/archive/html/bug-gettext/2012-12/msg00064.html>
<http://lists.gnu.org/archive/html/automake/2012-12/msg00024.html>
Commit v0.18.1.1-147-g2cccb4c in the Gettext git repository.

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