Renderer: Never use fog when drawing 3D player sprites

The player sprites are disjoint from the rest of the world in that
they use their own coordinate space that allows them to not Z-collide
into world surfaces. This means world fog is not applicable, as the
psprite Z distance has a different meaning than the world Z distance.
Merge branch 'master' of ssh://github.com/skyjake/Doomsday-Engine