push: move unqualified refname error into a function
A follow-up change will extend this error message with the advice
facility. Doing so would make the indentation too deeply nested for
comfort. So let's split this into a helper function.
There's no changes to the wording here. Just code moving &
re-indentation, and re-flowing the "TRANSLATORS" comment.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>