Rubik theme and group as required if it contains required fields

When you're using Rubik theme as admin, option "Mark group as required if it contains required fields." doesn't work for vertical tabs.

That caused by following code in base Tao theme:

/**
 * Implementation of preprocess_fieldset().
 */
function tao_preprocess_fieldset(&$vars) {
  // ...
  $vars['attributes']['class'][] = 'fieldset';
  // ...
}

It adds "fieldset" class for each fieldset on the page. Since vertical tabs content is being rendered as fieldset, function Drupal.FieldGroup.Effects.processTabs is never executed, because $('fieldset.fieldset') is processed by Drupal.FieldGroup.Effects.processFieldset. That happened because these 2 functions are using the same class for once() method.

I found an easy way how to fix that. We just should change class for once function.