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/unpack-objects.c

@@ -601,7 +601,10 @@ static void unpack_all(void)
 		die("unresolved deltas left after unpacking");
 }
 
-int cmd_unpack_objects(int argc, const char **argv, const char *prefix UNUSED)
+int cmd_unpack_objects(int argc,
+		       const char **argv,
+		       const char *prefix UNUSED,
+		       struct repository *repo UNUSED)
 {
 	int i;
 	struct object_id oid;