builtin: add a repository parameter for builtin functions

In order to reduce the usage of the global the_repository, add a
parameter to builtin functions that will get passed a repository
variable.

This commit uses UNUSED on most of the builtin functions, as subsequent
commits will modify the actual builtins to pass the repository parameter
down.

Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/ls-tree.c

@@ -329,7 +329,10 @@ static struct ls_tree_cmdmode_to_fmt ls_tree_cmdmode_format[] = {
 	},
 };
 
-int cmd_ls_tree(int argc, const char **argv, const char *prefix)
+int cmd_ls_tree(int argc,
+		const char **argv,
+		const char *prefix,
+		struct repository *repo UNUSED)
 {
 	struct object_id oid;
 	struct tree *tree;