Rewrite livery texture replacement to copy StateSet objects

Also, add a NodeAndDrawableVisitor that descends into osg::Drawable.

That motivation for this is that it's a bad idea to modify state sets
that the osgDB::SharedStateManager might be keeping.

simgear/screen/TestRenderTexture.cpp

@@ -16,6 +16,7 @@
 
 #include <assert.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 void Reshape(int w, int h);