blob: add repository argument to lookup_blob

Add a repository argument to allow the callers of lookup_blob
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>

walker.c

@@ -54,7 +54,8 @@ static int process_tree(struct walker *walker, struct tree *tree)
 				obj = &tree->object;
 		}
 		else {
-			struct blob *blob = lookup_blob(entry.oid);
+			struct blob *blob = lookup_blob(the_repository,
+							entry.oid);
 			if (blob)
 				obj = &blob->object;
 		}