Allow to sort by rating, which can be quite useful in combination with the "Show in Groups" feature. Although still slow, it basically works. All the code is based on Rafael Fernández López patch available at <a href="http://media.ereslibre.es/2007/06/dolphin-21062007.diff">http://media.ereslibre.es/2007/06/dolphin-21062007.diff.</a>;