#2 Lightning on terrain wrong with PM

[Marcus Lindblom Sonestedt]

Lightmap rendering on terrain while using the
progressive mesh isn't correct. The lightmaps appear
above or below terrain triangles.

Triangles fetched for lightmaps do not correspond to
those drawn while PM:ing. Need some alternative form
of lookup for this.

[Marcus Lindblom Sonestedt]

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This will be fixed with the new terrain-LOD system that
Truls is working on. ETA is 1-2 months away from now.