title: ajaxSubmit uploadProgress not responding
body: <p>I have a problem with the <code>$(a).AjaxSubmit</code> of <code>jQuery.Form</code>, with respect of option UploadProgress. This is my code:</p>
  
  <pre><code>$("#ifrm").contents().find("form").ajaxSubmit({
      data: { " + datos + " },
      target: "#sbmt",
      forceSync: true,
      uploadProgress: function(event, position, total, percentComplete) {
          alert(percentComplete);
      },
      success: function(html, status) {},
      complete: function(xhr) {
          if (xhr.statusText == "OK") {
              eval(xhr.responseText)
          }
          else {
              msgbox("Error en el Formulario", "Se produjo un error al subir el archivo.", 1);
              return false;
          }
      }
  });
  </code></pre>
  
  <p>The alert never appears. I need the event for a progress bar.</p>