Code that processed mouse wheel (track pad is reported as mouse wheel event)...

Code that processed mouse wheel (track pad is reported as mouse wheel event) was using an obsolete function, QWheelEvent::delete(), and it was replaced with QWheelEvent::pixelDelta() and QWheelEvent::angleDelta() as a fallback.  This seems to have fixed the sort oscillation that was noticed when trying to use the track pad on Macs.