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>

builtin/name-rev.c

@@ -379,7 +379,8 @@ static void name_rev_line(char *p, struct name_ref_data *data)
 			*(p+1) = 0;
 			if (!get_oid(p - (GIT_SHA1_HEXSZ - 1), &oid)) {
 				struct object *o =
-					lookup_object(oid.hash);
+					lookup_object(the_repository,
+						      oid.hash);
 				if (o)
 					name = get_rev_name(o, &buf);
 			}