[websocket] - allow the recv in pull to timeout else we might block when

calling mg_stop and having a websocket open.

This is more a RFC as it is not platform agnostic by using the Windows only WS define "WSAETIMEDOUT ". But it should be possible to do something similar to all other posix platforms aswell.

Background:
1. Create a websockert from the javascript side
2. Send some data through the socket
3. In the websocket_data callback return 1 so that civetweb keeps the socket open
4. Call mg_stop
5. See it deadlock because workerthread hangs in pull called from read_websocket

I don't mind any other approach for fixing the issue of course ;).