title: jetty exception and failed startup
body: <p>I upgrade gwt version from <code>2.3 to 2.7</code> and some other modules.
  maven build end successfully, but when I run in superDevMode get an exception</p>
  
  <pre class="lang-none prettyprint-override"><code>java.lang.IllegalArgumentException: Object of class 'com.google.gwt.dev.shell.jetty.JettyLauncher.WebAppContextWithReload' is not of type 'org.eclipse.jetty.webapp.WebAppContext'. Object Class and type Class are from different loaders.
  </code></pre>
  
  <p>I haven't any idea.</p>
  
  <p>Using:</p>
  
  <ul>
  <li>Intellij 14</li>
  <li>Jetty 9.3.12.v20160915</li>
  <li>Spring 4.3.3.RELEASE</li>
  <li>Servlet API 3.1.0</li>
  </ul>
  
  <pre class="lang-none prettyprint-override"><code>[WARN] Failed startup of context c.g.g.d.s.j.WebAppContextWithReload{/,file:/home/.../modules/core-war/target/x12/},/home/.../modules/core-war/target/x12
  java.lang.IllegalArgumentException: Object of class 'com.google.gwt.dev.shell.jetty.JettyLauncher.WebAppContextWithReload' is not of type 'org.eclipse.jetty.webapp.WebAppContext'. Object Class and type Class are from different loaders.
  at org.eclipse.jetty.xml.XmlConfiguration$JettyXmlConfiguration.configure(XmlConfiguration.java:323)
  at org.eclipse.jetty.xml.XmlConfiguration.configure(XmlConfiguration.java:281)
  at org.eclipse.jetty.webapp.JettyWebXmlConfiguration.configure(JettyWebXmlConfiguration.java:103)
  at org.eclipse.jetty.webapp.WebAppContext.configure(WebAppContext.java:468)
  at org.eclipse.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1237)
  at org.eclipse.jetty.server.handler.ContextHandler.doStart(ContextHandler.java:717)
  at org.eclipse.jetty.webapp.WebAppContext.doStart(WebAppContext.java:494)
  at com.google.gwt.dev.shell.jetty.JettyLauncher$WebAppContextWithReload.doStart(JettyLauncher.java:541)
  at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:64)
  at org.eclipse.jetty.server.handler.HandlerWrapper.doStart(HandlerWrapper.java:95)
  at org.eclipse.jetty.server.handler.RequestLogHandler.doStart(RequestLogHandler.java:162)
  at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:64)
  at org.eclipse.jetty.server.handler.HandlerWrapper.doStart(HandlerWrapper.java:95)
  at org.eclipse.jetty.server.Server.doStart(Server.java:282)
  at org.eclipse.jetty.util.component.AbstractLifeCycle.start(AbstractLifeCycle.java:64)
  at com.google.gwt.dev.shell.jetty.JettyLauncher.start(JettyLauncher.java:740)
  at com.google.gwt.dev.DevMode.doStartUpServer(DevMode.java:632)
  at com.google.gwt.dev.DevModeBase.startUp(DevModeBase.java:1054)
  at com.google.gwt.dev.DevModeBase.run(DevModeBase.java:836)
  at com.google.gwt.dev.DevMode.main(DevMode.java:413)
  </code></pre>