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* new: forward_for WAMP message attribute (for Crossbar.io Router-to-Router federation)
* new: support RawSocket URLs (eg "rs://localhost:5000" or "rs://unix:/tmp/file.sock")
* new: support WAMP-over-Unix sockets for WAMP components ("new API")
* fix: use same WAMP serializer construction code for WAMP components ("new API") and ApplicationSession/Runner
* fix: memory leak with Twisted/WebSocket, dropConnection and producer