// Set passed background-image to form type=submit just before ajax request was submitted.
// reset with ajax:complete.
// options:
// loadingImage: background-image
// loadingText: text
jQuery.fn.swapBackgroundToLoading = function(options){
  $(this).live('ajax:before', function(){
    var submit = $(this).find('input[type=submit]')
    var text = submit.val();
    var backgroundImage = submit.css('background-image');
    // set loading
    submit.val(options.loadingText || '');
    submit.css('background-image', 'url(' + loadingImagePath + ')');
    $(this).one('ajax:complete', function(){
      // reset
      submit.css('background-image', backgroundImage);
      submit.val(text);
    });
  });
};