Fix compatibility with Twisted 16.4.1 (and possibly earlier versions).
Fix compatibility with Twisted 16.4.1 (and possibly earlier versions).

Twisted now calls pauseProducing() when it finishes receiving the request.
For txsockjs to continue receiving data from the transport, it now needs to
call resumeProducing().  This should have no effect on earlier versions
of Twisted.

INTERACT-IV/sockjs-twisted,INTERACT-IV/sockjs-twisted,INTERACT-IV/sockjs-twisted