title: add parameters / query string values in action filter. c# mvc3
body: <p>When I attempt to add either parameters or query string values to the context inside an action filter, an exception gets raised to say that the collection is read only.</p>
  
  <p>I would like to add values to the 'outgoing' url when it is created.</p>
  
  <pre><code>filterContext.ActionParameters.Add("test", "test");
  </code></pre>
  
  <p>I need these values passed on to the query string, or in the request parameters.
  Thanks</p>