Multiple terrain texture blending.

  - after a 10 day slog finally have a texturing system that blends
    both for LOD (distance) and terrain type.
  - splatting was out of the question due to its impossible resource
    demands and the complexity of managing multiple alpha maps.
  - current system uses a terrain map that uses "r" values to track
    an integer terrain index.
  - the shaders then perform the necessary blending between terrain
    borders; the crux of the problem and what took so long:
    - tried for too long to look for a way to blend using tesselated
      tris when the solution (still fairly complex) is much more
      obvious if the original (non-tesselated) verts are used seed
      the border blending ratios.