Changed render_view_frustum() to handle broken camera yaw

* I discovered that the Camera class has a Yaw that is actually   180deg off of true yaw. So when the avatar is facing at a yaw   of 0deg, we were setting the camera to 180. This was causing   the direction vectors to be rotated from where we expected them   to be, and as a result the frustum was wrong 

* I did not fix the camera and the calls to glRotate() since I  don't yet understan how these work. BUT. I did fix the frustum  code to fix up this yaw before calculating the vectors