Tidy up drawFoliage function.
Vary foliage models.
Added some blue sky and tweaked some things.
Lowered sky plane and tweaked fog a bit more.
Fix sky plane depth testing.
Increase terrain complexity, large scale hills.
Reduce step size and fix some defines.
Increase foliage size and average ground height for collision detection.
Testing ground height detection, this works better.
Trying to prevent z-buffer fighting between foliage and terrain.  Needs more work.
Make sky plane end at fog end, looks smoother.