Bug fixes

• The WebSocketServer constructor now throws an error if more than one of the
  noServer, server, and port options are specefied (66e58d2).
• Fixed a bug where a 'close' event was emitted by a WebSocketServer before
  the internal HTTP/S server was actually closed (5a58730).
• Fixed a bug that allowed WebSocket connections to be established after
  WebSocketServer.prototype.close() was called (772236a).