Oculus rift

I'm issuing this pull request because I have spent way way too long trying to figure out how to update uniform shader parameters. Could you take a look at it and let me know if you see something wrong?

I modified oculusrift-barrel.fsh to promote "distortionScale" from a const to a uniform parameter.
I've tried to update the "distortionScale" uniform in vrcontenttransform.cpp, but I just get a runtime debug warning like:
#1044 14:11:34.310 (deb) GLProgram: Could not find uniform 'distortionScale' 
#1044 14:11:34.310 (deb) applyInProgram: 'distortionScale' not in the program 
and the shader parameter does not get changed.

Beware my most recent change set commented out something you probably want to keep. I commented out the lines so Doomsday could run on my machine.