Clip to bounding rect

Bounding rect varies from width/height in some cases, like Rectangle.

This restores rectangle clipping behaviour to be the same as QtQuick 1.

Task-number: QTBUG-20547
Change-Id: I2b6edc662a0026219d73b52878d2f4c046fef7f0
Reviewed-on: http://codereview.qt.nokia.com/2317


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Martin Jones <martin.jones@nokia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@nokia.com>