Changes made to add headtracking

vr_headtracking - 1 or 0. enable or disable headtracking
vr_driftcorrection - Slowly turns your view so that your center of view
is aligned with your head. Basically cancels out any drifting over time.
0.01 is nice and slow, you'll barely notice it. Most you should set it
to is 0.1, which move kinda fast. Anything above that starts to get
jerky.

you will need a compiled libovrwrapper.dll and libovrwrapper.lib, which
I have included, hopefully in the right place. I used "release" compile
settings.

If you want the source for libovrwrapper, it's in a different Visual
Studio version. Version 2010. It's a simple modification of vrquake3's
libovrwrapper, stripped of the sixense stuff. I will upload it later.