title: Add message to context.result
body: <p>I'm creating a DataAnnotation that if not successful will return a BadRequest.</p>
  
  <pre><code>context.Result = new BadRequestResult();
  </code></pre>
  
  <p>That works fine.</p>
  
  <p>I want to include a message along with this, but BadRequestResult doesn't appear to take any message params?</p>
  
  <p>Is there a way to do this...include a message to say e.g. "reference number not supplied" </p>
  
  <p>Thanks</p>