Convert struct cache_tree to use struct object_id

Convert the sha1 member of struct cache_tree to struct object_id by
changing the definition and applying the following semantic patch, plus
the standard object_id transforms:

@@
struct cache_tree E1;
@@
- E1.sha1
+ E1.oid.hash

@@
struct cache_tree *E1;
@@
- E1->sha1
+ E1->oid.hash

Fix up one reference to active_cache_tree which was not automatically
caught by Coccinelle.  These changes are prerequisites for converting
parse_object.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

revision.c

@@ -1249,7 +1249,7 @@ static void add_cache_tree(struct cache_tree *it, struct rev_info *revs,
 	int i;
 
 	if (it->entry_count >= 0) {
-		struct tree *tree = lookup_tree(it->sha1);
+		struct tree *tree = lookup_tree(it->oid.hash);
 		add_pending_object_with_path(revs, &tree->object, "",
 					     040000, path->buf);
 	}