title: Rails3 ajax callback has empty xhr
body: <p>I'm seeing some strange behaviour with my Rails3 app.  Note that I'm using the jQuery version of <code>rails.js</code></p>
  
  <p>From <code>rails.js</code> starting at line :49</p>
  
  <pre><code> error: function (xhr, status, error) {
     el.trigger('ajax:failure', [xhr, status, error]);
     alert('error in: ' + xhr.responseText ); 
   }
  </code></pre>
  
  <p>From my jQuery code to execute after the form.</p>
  
  <pre><code> .bind('ajax:failure', function(xhr, status, error) {
      alert('error in: ' + xhr.responseText );
   })
  </code></pre>
  
  <p>In the alert in rails.js shows the expected return text, but the alert my callback shows:</p>
  
  <pre><code>  error in: undefined
  </code></pre>
  
  <p>So it doesn't appear that xhr is being sent to the callback correctly.  Am I doing something wrong, or is this an issue with <code>rails.js</code>?</p>
  
  <p>Further testing shows that this applies for both the <code>ajax:failure</code> and <code>ajax:success</code> callbacks.  With the <code>ajax:success</code> call back the server response is in <code>status</code>, so I didn't notice the behavior.</p>