CID 1210936: use after free.
Fix handling of filled rectangles with transforms.

The DrawingEngine didn't properly make a distinction between the
rectangle being filled and the damaged region on screen. This led to
unexpected results when using BAffineTransform.
Transformation: add one more test

* Add test for a translation that makes things that are out of view
bounds to become visible
* Fix the "rectangles" test to handle scrolling of the view. It seems
that in some cases some of the rectangles are not drawn.

The gradient and bitmap tests currently have problem with view
scrolling, but I'm not sure why.