Improve Private Storage detection. MCabber now correctly detects Private Storage support when receiving an item-not-found error (which doesn't mean the server has no support for P.S., but that it's empty). I've added a return value to the callback functions. For now the return value is only used for IQ error handling.

 /CLEAR

Cette commande est en réalité un alias pour "/buffer clear". Elle efface la fenêtre de discussion sélectionnée.