title: FB.ui dialog for apprequest hangs forever in iframe mode
body: <p>Somehow I can't get the iframe mode to work in the following code 
  The dialog shows up but the loading hangs forever and nothing is displayed in the box
  it works just fine with display: popup</p>
  
  <pre><code>    FB.getLoginStatus(function(resp) {
  
        if (resp.status !== 'connected') return;
        FB.ui({
          method: 'apprequests',
          title: 'My title',
          display: 'iframe',
          message: 'My message',
          to: '100003750613973'
        }, function(resp) {
          console.log('emitted request to ', resp.to);
        });
      });
  </code></pre>