docs update, reference grid size correction to match default elevation layer tile size
Merge branch 'master' of github.com:gwaldron/osgearth
Made it so the OcclusionCullingCallback is based on the elevation and not range.

Made sure that the OcclusionCullingCallback is only intersecting with
the terrain and not the entire MapNode.
Merge branch 'master' of https://github.com/gwaldron/osgearth
Added text-occlusion-cull-elevation to the style sheets

Renamed max range functions/vars to max elevation in
OcclusionCullingCallback to reflect it's new implementation.
Added height adjustment setting for occlusion culling to AnnotationSettings.
Added docs for occlusion culling options.
Added feature_occlusion_culling example.
TileSource: docs, and a better name for minValidValue/maxValidValue
osgearth_cache: added docs for --index
Merge branch 'master' of github.com:gwaldron/osgearth
Normal transtion in LOD blending, step 1
LODBlending: support for basic normals
Updates to MPGeometry to support changes to OpenSceneGraph Geometry class in OSG 3.1.8
Merge branch 'master' of https://github.com/gwaldron/osgearth
Changed the order of some setColorBinding calls to be compatible with changes in OpenSceneGraph Geometry class..

You have to assign the array before modifying the binding.
Hooked back up vertical scale property in MP Engine TileModelCompiler.cpp
Added occlusion culling max altitude to IconSymbol; renamed elevation to altitude throughout OC code
Merge branch 'master' of github.com:gwaldron/osgearth
Added smart intersector handling to the OverlayNode to facilitate better intersections with overlay geometries.