Fix issue #11

[pmlt]

Removed the proxy actor of WebsocketFrontend by overriding
HttpServerConnection instead in SocketListener.

[lihaoyi]

Thanks for the patch! One question: the style of having separate actors was monkeyed blindly from the spray HTTP stack. Does that stack suffer the same problem? Or does it work around it in another way? Just want to get some context around the issue.

[pmlt]

Well, I haven't tested a pure Spray Can app to see if it exhibits the same problem, so maybe it does. But in principle, having a proxy actor isn't the problem itself; it's the fact that not all TCP event messages were proxied by the same actor. Technically, even with my patch SprayWebSockets still uses a proxy actor similar to Spray Can (namely SocketServerConnection) but at least now all TCP event messages go through that proxy actor.