revive the noPaintOnScreen fix on Windows

revive the noPaintOnScreen fix on Windows

The original commit message follows.

Fixes:   Fix the windows PaintOnScreen issue once and for all

Details: To allow both the case where X11 people accidentally set
         PaintOnScreen (which should not have any effect on windows)
         and where people set it and subclass with paintEngine() {
         return 0 } to use GDI / DirectX we do this rather nasty hack.

Original commit in Qt4: 07a2f68bd5869152471e4ffc4a63c683ef141ae8
Autotest: tst_QWidget::paintOnScreenPossible

Change-Id: Ifbb7dc4611959be3ecc362c29a1c3436b0e0fa82
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@nokia.com>