Added GeometryPool::s/getUseGeometryShader() hint, and OSG_TERRAIN_USE_GEOMETRY_SHADER env var for setting the default value.

git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14660 16af8721-9629-0410-8352-f15c8da7e697

include/osgTerrain/GeometryPool

@@ -110,6 +110,9 @@ class OSGTERRAIN_EXPORT GeometryPool : public osg::Referenced
 
         void applyLayers(osgTerrain::TerrainTile* tile, osg::StateSet* stateset);
 
+        void setUseGeometryShader(bool flag) { _useGeometryShader = flag; }
+        bool getUseGeometryShader() const { return _useGeometryShader; }
+
     protected:
         virtual ~GeometryPool();