title: GWTUpload add extra information
body: <p>I'm using the GWTUpload lib for uploading, which works nicely. On the server side I override the <code>executeAction()</code> method of the <code>UploadAction</code> class.</p>
  
  <p>But now I would somehow like to send some more information to the server e.g. to map the uploaded stuff to some user.</p>
  
  <p>I'm not using sessions to identify anybody. I would only want to pass a simple extra id from the client to the server while uploading.</p>
  
  <p>Can I modifiy the request parameters on the client side?</p>