refs.c: make ref_update_reject_duplicates take a strbuf argument for errors
refs.c: make ref_update_reject_duplicates take a strbuf argument for errors

Make ref_update_reject_duplicates return any error that occurs through a
new strbuf argument. This means that when a transaction commit fails in
this function we will now be able to pass a helpful error message back to the
caller.

Reviewed-by: Jonathan Nieder <b57189c5f2fd5b3daf3350a77fde90def1080fa5@gmail.com>
Signed-off-by: Ronnie Sahlberg <2cb6c6c4ccf58d41468189c2307f7a4ebf120324@google.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>
Acked-by: Michael Haggerty <c24c152f145c57791e809b126db9e61bd1c1782d@alum.mit.edu>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git