msgcat: Handle protected file names with spaces.
* gettext-tools/src/msgl-cat.c: Include msgl-ofn.h.
(catenate_msgdomain_list): Handle references that contain file names with
spaces.
* gettext-tools/tests/msgcat-22: New file, based on
gettext-tools/tests/msgconv-8.
* gettext-tools/tests/Makefile.am (TESTS): Add it.
