Add the “open” listener.
Remove mask on write-frames.

From RFC6455: “A server MUST NOT mask any frames that it sends to the
client. A client MUST close a connection if it detects a masked frame.”
This is fixed now.
[auto] Merge from Websocket

    • #a229d5d — Add the “open” listener. (Ivan Enderlin, 2013-02-26)
    • #31c810e — Remove mask on write-frames. (Ivan Enderlin, 2013-02-26)

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Merge remote branch 'library-websocket/master'