title: Use Websockets in GWT's DevMode
body: <p>has anyone an idea, how to run my app in DevMode with a working WebsocketConnection?
  First I thought the missing jetty jars (websocket, continuation, http, io, server and util) were the reason for errors, because when i compiled the app and put it on an external jetty, there was no problem with WebsocketConnection.
  So i searched for them and added them to my project. 
  But now everytime i start it in DevMode i get an exceptionlike this:</p>
  
  <pre><code>[WARN] /testchat/WebSocketChatServlet
  java.lang.NullPointerException
  at org.eclipse.jetty.websocket.WebSocketFactory.upgrade(WebSocketFactory.java:197)
  at org.eclipse.jetty.websocket.WebSocketFactory.acceptWebSocket(WebSocketFactory.java:304)
  at org.eclipse.jetty.websocket.WebSocketServlet.service(WebSocketServlet.java:78)
  at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
  at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
  at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362)
  at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
  at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
  at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729)
  at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
  at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
  at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49)
  at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
  at org.mortbay.jetty.Server.handle(Server.java:324)
  at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505)
  at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:829)
  at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:513)
  at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
  at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
  at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
  at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)
  </code></pre>
  
  <p>[ERROR] 500 - GET /testchat/WebSocketChatServlet (127.0.0.1) 3129 bytes</p>