refs: pass repo when peeling objects

Both `peel_object()` and `peel_iterated_oid()` implicitly rely on
`the_repository` to look up objects. Despite the fact that we want to
get rid of `the_repository`, it also leads to some restrictions in our
ref iterators when trying to retrieve the peeled value for a repository
other than `the_repository`.

Refactor these functions such that both take a repository as argument
and remove the now-unnecessary restrictions.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

object.h

@@ -288,7 +288,8 @@ enum peel_status {
  * or is not valid, return PEEL_NON_TAG or PEEL_INVALID, respectively,
  * and leave oid unchanged.
  */
-enum peel_status peel_object(const struct object_id *name, struct object_id *oid);
+enum peel_status peel_object(struct repository *r,
+			     const struct object_id *name, struct object_id *oid);
 
 struct object_list *object_list_insert(struct object *item,
 				       struct object_list **list_p);