We force writing a ref if it does not exist. Originally, we only had to look
for the ref file to check if it existed. Now we have to look for a packed ref
as well. Luckily, resolve_ref already does all the work for us.
Signed-off-by: Clemens Buchacher <drizzd@aon.at> Signed-off-by: Junio C Hamano <gitster@pobox.com>