/**
  * Removes a User from all groups  (adapted from WP-Group-Restriction plugin)
  *
  * @param int $user - User Identifier
  **/
 function delete_user_from_groups($user_id)
 {
     global $wpdb;
     // possible todo: pre-query user groups so we can do_action delete_group_user_rs
     $delete = "DELETE FROM {$wpdb->user2group_rs} WHERE {$wpdb->user2group_uid_col}='{$user_id}';";
     scoper_query($delete);
     ScoperAdminLib::flush_groups_cache_for_user($user_id);
 }