Cleanup the redis connection for pubsub when the client disconnects.

Because pubsub occupies the entire connection, we open a connection for
every client GET'ing the live stream. So the connection should be closed
should the client disconnects.
Be sure to FIN the stream if a POST'ing client disconnects.

A client POST'ing a stream may disconnect before the "end" of the
chunked request. If that happens, the stream needs to FIN so that
clients GET'ing the stream do not hang indefinitely.