title: MVC 3 RTM allowHtml doesn't work when using FormCollection
body: <p>MVC 3 RTM. Have a model that has an attribute with AllowHtml. In my controller action, if the action has FormCollection as parameter, it throws the exception:</p>
  
  <pre><code> [HttpPost]
   public ActionResult Edit(FormCollection collection, int id)
   {
     var myEntity = _myRepo.Get(id);
  
     TryUpdateModel(myEntity);
  
     return DoSave(myEntity);
   }
  </code></pre>
  
  <blockquote>
    <p>A potentially dangerous Request.Form
    value was detected from the client</p>
  </blockquote>
  
  <p>However if my controller action uses an object instead of FormCollection it doesn't throw the exception. </p>
  
  <pre><code> [HttpPost]
   public ActionResult Edit(MyEntity postedEntity, int id)
   {
     var myEntity = _myRepo.Get(id);
  
     TryUpdateModel(myEntity);
  
     return DoSave(myEntity);
   }
  </code></pre>
  
  <p>I've already setup</p>
  
  <blockquote>
    <p>httpRuntime
    requestValidationMode="2.0"</p>
  </blockquote>
  
  <p>Why does it fail when using FormCollection? </p>