REF00002: Forest regions do not follow terrain:
Tile.GetElevation(float x, float z) interpolates elevation based on Terrain's rendering to provide exact height of ground at the location.
ForestMesh.InitForestVertices() passes float coordinates for trees to GetElevation().
git-svn-id: http://svn.uktrainsim.com/svn/openrails/trunk@176 a9f3cfff-6c41-7446-b0ca-052bd761e6eb