Gettext 0.11.1: gettextize not idempotent

[Akim Demaille]

Hi!

There was a (maybe accidental) feature in previous versions of
Gettextize, namely that you could run it several times without
problems.  This property s precious, as it makes it possible for CVS
repository to not include the Gettext code: users just launch their
local autogen.sh, or autoreconf, or you name it.

I also regularly use autoreconf -f -v -i to upgrade a tree to newer
GNU Build System component, including gettext.

Unfortunately there are now weird side effects:

- it keeps adding intl/Makefile in the first AC_CONFIG_FILES that does not
  contain it already.

- it keeps adding its three .m4 files in EXTRA_DIST in m4/Makefile.

I think there were others, but I lost track of them.

The first one is quite easy to fix, I'd say that grepping for
intl/Makefile in configure.(in|ac) is way enough.  The second one can
be addressed the same way.