Cosmetic changes based on feedback on PR #506.
D3D: Don't set the windowed mode size when we initialize in fullscreen.
Renderer: Resize the window by communicating with the UI thread.
Renderer: Don't attempt to switch to exclusive fullscreen if "render to main" is enabled.
VideoConfig: Replace "3D Vision" by "Borderless Fullscreen" option.

This option will disable exclusive fullscreen for users who prefer the old behaviour.

Also remove the 3D Vision hack that should no longer be necessary.
CFrame: Don't reassign focus when we're not rendering to the main window.
Frame: Fix RendererHasFocus() again.