JSR-356 fixing calling of @OnMessage with partial message boolean
JSR-356 fixing NPE on bufferPool
Testing for non-null
WebSocket - better protection on metadata cache
WebSocket - breaking out unfinished MUX extension into its own module
WebSocket - supporting WriteCallback in jetty RemoteEndpoint

+ new RemoteEndpoint.sendBytes(ByteBuffer, WriteCallback)
+ new RemoteEndpoint.sendString(String, WriteCallback)