Add preliminary support for VR/OpenVR for HTC Vive and Oculus Rift,

(Windows-only first, later Linux and OSX)
Use premake to build, use --enable_openvr flag

examples/OpenGLWindow/GLInstancingRenderer.h

@@ -132,6 +132,7 @@ public:
     }
 	virtual void clearZBuffer();
 
+	virtual void setRenderFrameBuffer(unsigned int renderFrameBuffer);
 };
 
 #endif //GL_INSTANCING_RENDERER_H