* Fix issue with add transparency mode with blender materials.
* Possible fix at frontface flip in the game engine.
* Fix color buffering clearing for multiple viewports, it used
to clear as if there was one.
* Fix for zoom level in user defined viewports, it was based on
the full window before, now it is based on the viewport itself.
* For user defined viewports, always use Expose instead of
Letterbox with bars, the latter doesn't make sense then.
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