on_download_finished signal is not correctly used in the Windows IPC

The following errors are spawned when using ubuntu one control panel on windows:

Peer will receive following PB traceback:
Traceback (most recent call last):
  File "twisted\spread\banana.pyc", line 153, in gotItem

  File "twisted\spread\banana.pyc", line 116, in callExpressionReceived

  File "twisted\spread\pb.pyc", line 514, in expressionReceived

  File "twisted\spread\pb.pyc", line 826, in proto_message

--- <exception caught here> ---
  File "twisted\spread\pb.pyc", line 840, in _recvMessage

  File "twisted\spread\flavors.pyc", line 114, in remoteMessageReceived

  File "ubuntuone\platform\windows\ipc_client.pyc", line 58, in callback_wrapper

exceptions.TypeError: on_download_finished() takes exactly 2 arguments (3 given)