Displays the Build Group form.
public function buildGroupForm($form, &$form_state) {
$item =& $this->options;
// flip. If the filter was a group, set back to a standard filter.
$item['is_grouped'] = empty($item['is_grouped']);
// If necessary, set new defaults:
if ($item['is_grouped']) {
$this
->buildGroupOptions();
}
$form_state['view']
->get('executable')
->setItem($form_state['display_id'], $form_state['type'], $form_state['id'], $item);
$form_state['view']
->addFormToStack($form_state['form_key'], $form_state['display_id'], $form_state['type'], $form_state['id'], TRUE, TRUE);
$form_state['view']
->cacheSet();
$form_state['rerender'] = TRUE;
$form_state['rebuild'] = TRUE;
$form_state['force_build_group_options'] = TRUE;
}