peer: raise NotImplementedError for abstract submit() method

Nothing should ever call this submit method directly as it should be
overridden by concrete batcher implementations.

mercurial/peer.py

@@ -39,7 +39,7 b' class batcher(object):'
             return resref
         return call
     def submit(self):
-        pass
+        raise NotImplementedError()
 
 class localbatch(batcher):
     '''performs the queued calls directly'''