Fix gettext problems

GNOME's pre-commit hooks discovered a couple of gettext problems in
three translations.  This removes (by hand) the c-format specifiers
that were causing the problem as well as adds the no-c-format comments
in the code so the problem doesn't happen again.

Finally, msgfmt -c is now used to catch these errors in the future,
although the Makefile doesn't abort (like it should) when that
happens.  More work necessary for that.