QTabBar: Disable wheel events on Mac

Many people complain about this unexpected behavior. We
may consider introducing a style hint later for those
few people that may want it.

Change-Id: Ifab663b4b5c3a78a3544ab4408cf34f672df8c05
Task-number: QTBUG-8428
Reviewed-by: Timur Pocheptsov <Timur.Pocheptsov@digia.com>

src/widgets/widgets/qtabbar.cpp

@@ -2031,10 +2031,12 @@ void QTabBar::keyPressEvent(QKeyEvent *event)
 #ifndef QT_NO_WHEELEVENT
 void QTabBar::wheelEvent(QWheelEvent *event)
 {
+#ifndef Q_OS_MAC
     Q_D(QTabBar);
     int offset = event->delta() > 0 ? -1 : 1;
     d->setCurrentNextEnabledIndex(offset);
     QWidget::wheelEvent(event);
+#endif
 }
 #endif //QT_NO_WHEELEVENT