* origin/topic/awelzel/4440-websocket-pong-timeout:
btest/cluster/websocket: Update tests for new event signature
cluster/websocket: Propagate code and reason to websocket_client_lost()
cluster/websocket: Support configurable ping interval
IXWebSocket: Bump to improve O^2 rxbuf erase()
(cherry picked from commit 8f60d37ad0)
Explicitly notify the internal thread about the shutdown via the
inproc socket pair. This ensures that the internal thread processes
all previous messages on the inproc socket before terminating.
This fixes the scenario where a backend is created, a few messages published
and then immediately terminated as can be done with WebSocket clients.
Previously, some of the messages published might have still been in the
inproc socket's queue and were simply discarded.
Adds the same test for Broker and ZeroMQ backends.
