tag: add repository argument to lookup_tag

Add a repository argument to allow the callers of lookup_tag
to be more specific about which repository to act on. This is a small
mechanical change; it doesn't change the implementation to handle
repositories other than the_repository yet.

As with the previous commits, use a macro to catch callers passing a
repository other than the_repository at compile time.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

object.c

@@ -223,7 +223,7 @@ struct object *parse_object_buffer_the_repository(const struct object_id *oid, e
 			obj = &commit->object;
 		}
 	} else if (type == OBJ_TAG) {
-		struct tag *tag = lookup_tag(oid);
+		struct tag *tag = lookup_tag(the_repository, oid);
 		if (tag) {
 			if (parse_tag_buffer(tag, buffer, size))
 			       return NULL;