ref-filter: factor out "%(foo) does not take arguments" errors

ref-filter: factor out "%(foo) does not take arguments" errors

Many atom parsers give the same error message, differing only in the
name of the atom. If we use "%s does not take arguments", that should
make life easier for translators, as they only need to translate one
string. And in doing so, we can easily pull it into a helper function to
make sure they are all using the exact same string.

I've added a basic test here for %(HEAD), just to make sure this code is
exercised at all in the test suite. We could cover each such atom, but
the effort-to-reward ratio of trying to maintain an exhaustive list
doesn't seem worth it.

Signed-off-by: Jeff King <peff@peff.net>
Acked-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>