Support Quad-Buffered stereoscopy.

This is the ideal stereoscopy mode that is officially supported in both the OpenGL and DirectX API. This mode is only supported on Nvidia Quadro cards and AMD cards from Radeon HD 6000 series and up.

This mode is also known as AMD HD3D, which is the competitor of Nvidia 3D Vision.

This PR should be tested thoroughly, though I'm not sure if anyone has the necessary hardware.