websockets: turn on autoPingInterval to expire stale connections

With this, both clients and servers will send a PING at least once every
minute, and will drop connections that haven't seen any traffic for 10
minutes.

This should help keep NAT table entries alive, and will drop connections
that are no longer viable because their NAT entries have expired.

closes #60

src/wormhole/server/rendezvous_websocket.py

@@ -247,5 +247,6 @@ class WebSocketRendezvousFactory(websocket.WebSocketServerFactory):
     protocol = WebSocketRendezvous
     def __init__(self, url, rendezvous):
         websocket.WebSocketServerFactory.__init__(self, url)
+        self.setProtocolOptions(autoPingInterval=60, autoPingTimeout=600)
         self.rendezvous = rendezvous
         self.reactor = reactor # for tests to control

src/wormhole/wormhole.py

@@ -354,6 +354,7 @@ class _Wormhole:
         self._ws_t = self._timing.add("open websocket")
         p = urlparse(self._ws_url)
         f = WSFactory(self._ws_url)
+        f.setProtocolOptions(autoPingInterval=60, autoPingTimeout=600)
         f.wormhole = self
         f.d = defer.Deferred()
         # TODO: if hostname="localhost", I get three factories starting