Fix channel closed callback signature in the Twisted adapter.

The callback function for closed channel events receives a Method
frame.
Don't stop the IOLoop on connection close for in the Twisted adapter.

Typical Twisted programs will not want to have their reactor stopped
just because the Rabbit connection has been closed.
Merge pull request #292 from wulczer/channel-closed-and-ioloop-stop

Fix channel_close in Twisted adapter and don't stop IOLoop