refs: teach arbitrary repo support to iterators

Note that should_pack_ref() is called when writing refs, which is only
supported for the_repository, hence the_repository is hardcoded there.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -255,12 +255,13 @@ int refname_is_safe(const char *refname)
  * does not exist, emit a warning and return false.
  */
 int ref_resolves_to_object(const char *refname,
+			   struct repository *repo,
 			   const struct object_id *oid,
 			   unsigned int flags)
 {
 	if (flags & REF_ISBROKEN)
 		return 0;
-	if (!has_object_file(oid)) {
+	if (!repo_has_object_file(repo, oid)) {
 		error(_("%s does not point to a valid object!"), refname);
 		return 0;
 	}