Immutable chain/chord

Conflicts:
	celery/canvas.py

celery/canvas.py

@@ -604,7 +604,8 @@ class chord(Signature):
     def apply_async(self, args=(), kwargs={}, task_id=None,
                     producer=None, publisher=None, connection=None,
                     router=None, result_cls=None, **options):
-        args = tuple(args) + tuple(self.args) if args else self.args
+        args = (tuple(args) + tuple(self.args)
+                if args and not self.immutable else self.args)
         body = kwargs.get('body') or self.kwargs['body']
         kwargs = dict(self.kwargs, **kwargs)
         body = body.clone(**options)