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>
diff --git a/builtin/replace.c b/builtin/replace.c
index 0232f98..0351b7c 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c
@@ -402,7 +402,7 @@ static int check_one_mergetag(struct commit *commit,
 	int i;
 
 	hash_object_file(extra->value, extra->len, type_name(OBJ_TAG), &tag_oid);
-	tag = lookup_tag(&tag_oid);
+	tag = lookup_tag(the_repository, &tag_oid);
 	if (!tag)
 		return error(_("bad mergetag in commit '%s'"), ref);
 	if (parse_tag_buffer(tag, extra->value, extra->len))