Added support for fine grained computation of the near plane, by taking

into account individual primitives culled against the view frustum.

Added better support for computing the near far for billboards.

src/osgUtil/SceneView.cpp

@@ -37,6 +37,7 @@ SceneView::SceneView(DisplaySettings* ds)
     _clearColor.set(0.2f, 0.2f, 0.4f, 1.0f);
 
     _computeNearFar = CullVisitor::COMPUTE_NEAR_FAR_USING_BOUNDING_VOLUMES;
+    //_computeNearFar = CullVisitor::COMPUTE_NEAR_FAR_USING_PRIMITIVES;
 
     _cullingMode = osg::CullStack::DEFAULT_CULLING;
     _LODScale = 1.0f;