Before it would get stuck forever in "backup running" state. Now it aborts and displays to the user why.
Also, don't try to check content... no way for QMimeDatabase to access repo data, need kio for that.
It was not shown in the Qt 4 days, let's not show it now either.
Also sneak in a nicer way to launch kup-filedigger.
Needed now that KDirSelectDialog has been removed.