ignore/delete older translations

esp. usefull with nightly builds and self built versions, saves us from having to manually delete translations that had been upfdated for an earlier build, but are not used because the 'make lrelease' step creates and the 'make instll' stepp bundlle older Version but with a nerer timesept, so that These take precence when loading the Translation.
Probably only one of the commits is really needed...