Various minor PLBVH related changes.

-Use most significant bit instead of negative for internal nodes.
-Explicitly store root node index, so that it does not have to be 0.
-Check the root node first in PLBVH traversal.
-Fix rigid body clipping in RaytracedShadowDemo.

Demos3/GpuDemos/raytrace/RaytracedShadowDemo.cpp

@@ -187,6 +187,10 @@ void GpuRaytraceScene::renderScene()
 
 void GpuRaytraceScene::renderScene2()
 {
+	//If using the BVH to accelerate raycasting, the AABBs need to be updated or else they will
+	//not match the actual rigid body positions after integration. The result is that rigid bodies
+	//are not drawn or appear clipped, especially if they are moving quickly.
+	m_data->m_rigidBodyPipeline->setupGpuAabbsFull();
 	
 //	GpuBoxPlaneScene::renderScene();
 //	return;