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>

object.h

@@ -109,7 +109,8 @@ extern struct object *get_indexed_object(unsigned int);
  * half-initialised objects, the caller is expected to initialize them
  * by calling parse_object() on them.
  */
-struct object *lookup_object(const unsigned char *sha1);
+#define lookup_object(r, s) lookup_object_##r(s)
+struct object *lookup_object_the_repository(const unsigned char *sha1);
 
 extern void *create_object(struct repository *r, const unsigned char *sha1, void *obj);