calm down -Wdelete-non-virtual-dtor warnings

remove -Wno-non-virtual-dtor from makefile (what does it do anyway? -Wdelete-non-virtual-dtor is part of -Wall)

radiant/scenegraph.cpp

@@ -65,7 +65,7 @@ TypeId getTypeId( const char* name ){
 }
 };
 
-class CompiledGraph : public scene::Graph, public scene::Instantiable::Observer
+class CompiledGraph final : public scene::Graph, public scene::Instantiable::Observer
 {
 typedef std::map<PathConstReference, scene::Instance*> InstanceMap;