Tiding up the _AMAZING_ patch proposed by John Tapsell. His idea was to place the categories by an int instead of a boolean, depending on if the value is negative, 0 or positive you know that the category is before, the same, or after for two given indexes.

This simplifies amazingly the KCategorizedSortFilterProxyModel. This patch is fundamental for .0. We get rid out of some annoying bugs, so this is a bugfix also (like selections when changing sortings not being kept correctly).