A subsequent change will make use of this static function in the
get_short_oid() function, which is defined above where the
collect_ambiguous() function is now. Without this we'd then have a
compilation error due to a forward declaration.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>