Timewarp: Add option to warp 20/30/60fps->75fps.
Timewarp pullup headtracking isn't as good as the opcode replay buffer, but is stable unlike the replay buffer.
Merge pull request #16 from CarlKenner/VR-Hydra

More stuff
VR Button: Disable other timewarp/opcode replay options if one is already selected.
Remove VR tab from Graphics dialog, default Vignette to 'true' if the SDK!= 0.4.3
Fix hangs on close related to AsyncTimewarp functions getting called instead of the desired ones
Correct some GCC warnings, allow for autovectorization
Revert "Remove VR tab from Graphics dialog, default Vignette to 'true' if the SDK!= 0.4.3"

This reverts commit 138f7a87b54ee7d777e1431c273d46761ca26726.