Remove the 3D Vision hack.

The hack was needed because the Nvidia 3D Vision heuristics are documented to only support surfaces that are the same size as the backbuffer. This would be the case if you enabled the hack and selected the "Auto (Window Size)" internal resolution.

However, on recent drivers the same effect is achieved by selecting the "Auto (Multiple)" internal resolution. Therefore the hack is no longer required.
CFrame: Prevent fullscreen switches if the renderer is halted.
Cosmetic changes based on feedback on PR #506.
D3D: Make the global swapchain static again.