Clean up connections after connection closed #504

/**
 * Start the connection lost timer
 */
protected void startConnectionLostTimer() {
    if (this.connectionLostTimeout <= 0) {
        if (WebSocketImpl.DEBUG)
            System.out.println("Connection lost timer deactivated");
        return;
    }
    if (WebSocketImpl.DEBUG)
        System.out.println("Connection lost timer started");
    cancelConnectionLostTimer();
    connectionLostTimer = new Timer();
    connectionLostTimerTask = new TimerTask() {
        @Override
        public void run() {
            Collection<WebSocket> con = connections();
            synchronized ( con ) {
                long current = (System.currentTimeMillis()-(connectionLostTimeout * 1500));
                for( WebSocket conn : con ) {
                    if (conn instanceof WebSocketImpl) {
                        if( ((WebSocketImpl)conn).getLastPong() < current ) {
                            if (WebSocketImpl.DEBUG)
                                System.out.println("Closing connection due to no pong received: " + conn.toString());
                            conn.close( CloseFrame.ABNORMAL_CLOSE );
                        } else {
                            conn.sendPing();
                        }
                    }
                }
            }
        }
    };
    connectionLostTimer.scheduleAtFixedRate( connectionLostTimerTask,connectionLostTimeout * 1000, connectionLostTimeout * 1000 );
}