Make "tree_entry" have a SHA1 instead of a union of object pointers

This is preparatory work for further cleanups, where we try to make
tree_entry look more like the more efficient tree-walk descriptor.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

revision.c

@@ -68,9 +68,9 @@ void mark_tree_uninteresting(struct tree *tree)
 	while (entry) {
 		struct tree_entry_list *next = entry->next;
 		if (entry->directory)
-			mark_tree_uninteresting(entry->item.tree);
+			mark_tree_uninteresting(lookup_tree(entry->sha1));
 		else
-			mark_blob_uninteresting(entry->item.blob);
+			mark_blob_uninteresting(lookup_blob(entry->sha1));
 		free(entry);
 		entry = next;
 	}