fix unstable VRectangle / VCircle contains calculation.

see issue #322 (closed)

For specific combinations of rectangles and circles, the generic containsShape() method which builds on the AWT Area class hangs in an endless loop. This is most likely rooted in the problem that a circle is approximated by bezier curves in the Area class and this causes numerical instabilities.

This fix only is implemented in the VRectangle class for now. Other VShape objects still use the old (numerical instable) containsShape implementation (which is based on AWT's Area class).