object: add repository argument to lookup_object

Add a repository argument to allow callers of lookup_object to be more
specific about which repository to handle. 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: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

reachable.c

@@ -108,7 +108,7 @@ static int add_recent_loose(const struct object_id *oid,
 			    const char *path, void *data)
 {
 	struct stat st;
-	struct object *obj = lookup_object(oid->hash);
+	struct object *obj = lookup_object(the_repository, oid->hash);
 
 	if (obj && obj->flags & SEEN)
 		return 0;
@@ -133,7 +133,7 @@ static int add_recent_packed(const struct object_id *oid,
 			     struct packed_git *p, uint32_t pos,
 			     void *data)
 {
-	struct object *obj = lookup_object(oid->hash);
+	struct object *obj = lookup_object(the_repository, oid->hash);
 
 	if (obj && obj->flags & SEEN)
 		return 0;