Various game engine fixes:

* 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.

source/gameengine/Rasterizer/RAS_OpenGLRasterizer/RAS_OpenGLRasterizer.h

@@ -88,7 +88,6 @@ class RAS_OpenGLRasterizer : public RAS_IRasterizer
 	float			m_focallength;
 	bool			m_setfocallength;
 	int				m_noOfScanlines;
-	bool			InterlacedStereo() const;
 
 	//motion blur
 	int	m_motionblur;
@@ -131,6 +130,7 @@ public:
 	virtual bool	Init();
 	virtual void	Exit();
 	virtual bool	BeginFrame(int drawingmode, double time);
+	virtual void	ClearColorBuffer();
 	virtual void	ClearDepthBuffer();
 	virtual void	ClearCachingInfo(void);
 	virtual void	EndFrame();
@@ -138,6 +138,7 @@ public:
 
 	virtual void	SetStereoMode(const StereoMode stereomode);
 	virtual bool	Stereo();
+	virtual bool	InterlacedStereo();
 	virtual void	SetEye(const StereoEye eye);
 	virtual StereoEye	GetEye();
 	virtual void	SetEyeSeparation(const float eyeseparation);