Improve Qt detection in the build system (#160)
Improve Qt detection in the build system (#160)

It now correctly finds the system-wide Qt installation on GNU/Linux
and actually verifies whether the QTDIR variable is set correctly.
KNTGPolygon/PolyEngine,PiotrMoscicki/PolyEngine,KNTGPolygon/PolyEngine,PiotrMoscicki/PolyEngine