Since b8e30215 KDEVELOP_VERSION_PATCH is
greater than 255 (e.g. 220770). The way KDEV_ITEMREPOSITORY_VERSION is
currently calculated assumes that KDEVELOP_VERSION_PATCH is less than or
equal to 255. Otherwise, the values of KDEV_ITEMREPOSITORY_VERSION
calculated for different KDevelop versions may coincide.

This commit resolves the potential issue by making
KDEV_ITEMREPOSITORY_VERSION depend only on the major and the minor
KDevelop versions. This has an extra benefit of clearing data
repositories less often. The item repository format shouldn't change in
patch versions anyway. On the unlikely occasion it does change, the
responsible developer should remember to bump the
KDEV_ITEMREPOSITORY_INCREMENT variable.