Added new osg::OccluderNode which subclasses from osg::Group, and will

provide hooks for adding ConvexPlanerOccluders to the scene.

src/osg/OccluderNode.cpp

@@ -0,0 +1,13 @@
+#include <osg/OccluderNode>
+
+using namespace osg;
+
+OccluderNode::OccluderNode()
+{
+}
+
+OccluderNode::OccluderNode(const OccluderNode& node,const CopyOp& copyop):
+    Group(node,copyop),
+    _occluder(dynamic_cast<ConvexPlanerOccluder*>(copyop(node._occluder.get())))
+{
+}