title: FB.Event.subscribe not working for method: 'send'
body: <p>I'm using <code>FB.ui</code> to create a send dialog... I'm trying to get a callback after the user sent  the message, but it's not working for some reason.</p>
  
  <p>I tried to use <code>FB.event.subscribe</code></p>
  
  <pre><code>   FB.ui({                                                                                                                                                                   
       method: 'send',                                                                                                                                                         
       name: 'You\'re invited to join!',                                                                                                                          
       link: 'http://anexample.com',                                                                                                                                                              
     }); 
  
     FB.Event.subscribe('message.send',                                                                                                                                          
        function(response){                                                                                                                                                      
         alert('You sent a message from the URL ' + response);                                                                                                                                 
       }                                                                                                                                                                         
    );
  </code></pre>
  
  <p>Could anyone tell me what could be the problem with the subscribe ? The send works just fine.</p>