Added CullingUtils::ProxyCullVisitor that lets you run a cull pass on a subgraph using a proxy frustum (to support clamping); Various speedups and improvements to the OverlayDecorator; Integrated ECEF into SpatialReference (call srs->getECEF() and do normal transform calls); Fixes to the ECEF calculations to account for differing ellipsoids during transformation; Improvements to the edge-normalization in quadtree when sample_ratio != 1.