tree: add repository argument to lookup_tree

Add a repository argument to allow the callers of lookup_tree
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/list-objects.c b/list-objects.c
index 04c45f6..782c0e1 100644
--- a/list-objects.c
+++ b/list-objects.c
@@ -158,7 +158,7 @@ static void process_tree(struct rev_info *revs,
 
 		if (S_ISDIR(entry.mode))
 			process_tree(revs,
-				     lookup_tree(entry.oid),
+				     lookup_tree(the_repository, entry.oid),
 				     show, base, entry.path,
 				     cb_data, filter_fn, filter_data);
 		else if (S_ISGITLINK(entry.mode))