title: GWT development mode issue
body: <p>I'm running a GWT app in a dev mode with a custom Jetty container. The app loads fine for the first time, however, if I refresh it, I get the following errors in the Development Mode window (paths changed):</p>
  
  <pre><code>00:16:44.854 [ERROR] Unable to create file 'C:\somePath\src\war\msjavaSnack\C4EA130FD0ED44BE513FEEDDE13614DA.cache.png'
  java.io.FileNotFoundException: C:\somePath\src\war\msjavaSnack\C4EA130FD0ED44BE513FEEDDE13614DA.cache.png (The requested operation cannot be performed on a file with a user-mapped section open) 
  at java.io.FileOutputStream.open(Native Method) 
  at java.io.FileOutputStream.&lt;init&gt;(FileOutputStream.java:194) 
  at java.io.FileOutputStream.&lt;init&gt;(FileOutputStream.java:145) 
  at com.google.gwt.core.ext.linker.impl.StandardLinkerContext.writeArtifactToFile(StandardLinkerContext.java:658) 
  at com.google.gwt.core.ext.linker.impl.StandardLinkerContext.produceOutputDirectory(StandardLinkerContext.java:595) 
  at com.google.gwt.dev.DevMode.produceOutput(DevMode.java:476) 
  at com.google.gwt.dev.DevModeBase.relink(DevModeBase.java:1131) 
  at com.google.gwt.dev.DevModeBase.access$000(DevModeBase.java:67) 
  at com.google.gwt.dev.DevModeBase$2.accept(DevModeBase.java:1076) 
  at com.google.gwt.dev.shell.ShellModuleSpaceHost$1.accept(ShellModuleSpaceHost.java:122) 
  at com.google.gwt.dev.shell.StandardRebindOracle$Rebinder.rebind(StandardRebindOracle.java:59) 
  at com.google.gwt.dev.shell.StandardRebindOracle.rebind(StandardRebindOracle.java:154) 
  at com.google.gwt.dev.shell.ShellModuleSpaceHost.rebind(ShellModuleSpaceHost.java:119) 
  at com.google.gwt.dev.shell.ModuleSpace.rebind(ModuleSpace.java:531) 
  at com.google.gwt.dev.shell.ModuleSpace.rebindAndCreate(ModuleSpace.java:414) 
  at com.google.gwt.dev.shell.GWTBridgeImpl.create(GWTBridgeImpl.java:39) 
  at com.google.gwt.core.client.GWT.create(GWT.java:98) 
  at com.extjs.gxt.ui.client.GXT.&lt;clinit&gt;(GXT.java:38) 
  at com.extjs.gxt.ui.client.widget.Component.&lt;clinit&gt;(Component.java:202) 
  at msjava.snack.gui.client.MSHeaderPanelViewport.&lt;init&gt;(MSHeaderPanelViewport.java:62) 
  at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) 
  at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) 
  at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) 
  at java.lang.reflect.Constructor.newInstance(Constructor.java:513) 
  at com.google.gwt.dev.shell.ModuleSpace.rebindAndCreate(ModuleSpace.java:422) 
  at com.google.gwt.dev.shell.ModuleSpace.onLoad(ModuleSpace.java:361) 
  at com.google.gwt.dev.shell.OophmSessionHandler.loadModule(OophmSessionHandler.java:185) 
  at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:380) 
  at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:222) 
  at java.lang.Thread.run(Thread.java:662)
  </code></pre>
  
  <p><strong>UPDATE</strong></p>
  
  <p>In the ProcessExplorer I can see that the JVM process hosting Jetty has an open handle to the file so this is probably the reason why the other JVM (hosting the dev mode) can't write to it. Any way to work it around?</p>