nls: Add all man pages to pot file

nls: Add all man pages to pot file

The previous Makefile rule would only put the first required file
into the pot file because it used $< Unfortunately, due to how
po4a tools work, its not just a simple matter of changing it to $^
and you're done, but needs a foreach loop to add -m to each manpage
file.

This is a temporary fix, after some more work looking into po4a the
unified tool (called po4a) will be used.