msgmerge must produce output that is stable under msgcat.

msgmerge must produce output that is stable under msgcat.

Reported by Ludovic Courtès <ludo@gnu.org>
in <https://savannah.gnu.org/bugs/?51027>.

* gettext-tools/src/write-po.c (message_print_obsolete): Preserve the 'no-wrap'
and '*-format' flags.
* gettext-tools/tests/msgmerge-27: New file.
* gettext-tools/tests/msgmerge-28: New file.
* gettext-tools/tests/Makefile.am (TESTS): Add them.
* gettext-tools/tests/msgmerge-19: Update expected result.