title: jQuery-File-Upload iframe fallback detection
body: <p>Using blueimp's jQuery-File-Upload at <a href="https://github.com/blueimp/jQuery-File-Upload" rel="nofollow">https://github.com/blueimp/jQuery-File-Upload</a></p>
  
  <p>My application is running on many older browsers. File uploading has a long list of compatibility constraints.
  I'd like to simply detect when the fileuploader has gracefully fallen back to using iframe transport.
  I would like to detect this in the jQuery where the fileupload is being used similar to this example:</p>
  
  <pre><code>var using_iframe_transport = false;
  
  this_file_input.fileupload({
    dataType: 'json',
    url: "http://api.cloudinary.com/v1_1/my_account/image/upload",
  
    //as we send the file upload, record whether it is using iframe
    send: function (e, data) {
      if (e.iframe_fallback){ //is there a variable like this that exists in the plugin?
        using_iframe_transport = true;
      }
    }
  });//end fileupload
  
  if (using_iframe_transport){
    //do something
  }
  </code></pre>
  
  <p>It is possible to use this code in the 'progress', 'done', or 'always' callback:</p>
  
  <pre><code>...
    progress: function(e){ //or 'done' or 'always'
      if($('iframe').length){
        using_iframe_transport = true;
      }
    }
  ...
  </code></pre>
  
  <p>However these callbacks are not always made as reported at <a href="https://github.com/blueimp/jQuery-File-Upload/issues/461#issuecomment-9299307" rel="nofollow">https://github.com/blueimp/jQuery-File-Upload/issues/461#issuecomment-9299307</a></p>
  
  <p>My biggest concerns are supporting IE6 and Android 2.3 default browser. Thanks!</p>