Fix transforms (except that a -90 degree rotation of tests/transforms.png, followed by Undo nukes most of the transparency -- will investigate after this commit):

* Fix flipping and rotating-by-multiples-of-90-degrees being off by 1 pixel, by using QPixmap::trueMatrix() and for flipping, using TransformPixmap() instead of QPixmap::transformed()

* Use the abstract kpPixmapFX::draw() pattern to not ruin the no-alpha-channel invariant in TransformPixmap() [previously called xForm()]

* Verify that all of this file has been ported to Qt4 and fix style, comments etc.

This took hours and hours to write and debug (and I still have more debugging to do as per above) so I hope you like it :)