Trial Mountain 3.1

This started out as a simple bug fix, but got carried away.

Here's whats new:
* Grass and forest ground cover to give the track a lush green look.
* Rebuilt the walls for more accurate collisions. A few more crash fences.
* Quick-play is now available, with reverse and rolling starts.
* Access roads have been carved out around the track to reach spectator areas and for exploring.
* Newly built 3D curbs at the apexes will make corner cutting more difficult - especially at Turn 1.
* Tunnel Lighting
* Smoothed the track surface to decrease stuttering.
- Fixed all of the potholes in the terrain.
- Fixed the black dirt terrain spots.

Up next update: new grand stands, more spectators, and night lighing.