Fixed compilation error in src/osgDB/FileUtils.cpp.

Added support for nested NodeCallbacks, allowing them to be chained together
so that multiple operations can be applied.

src/Demos/osgcube/osgcube.cpp

@@ -57,7 +57,7 @@ class TransformCallback : public osg::NodeCallback{
             }
             
             // must continue subgraph traversal.
-            nv->traverse(*node);            
+            traverse(node,nv);            
             
         }
         

src/Demos/osgreflect/osgreflect.cpp

@@ -84,8 +84,7 @@ class TransformCallback : public osg::NodeCallback{
             }
             
             // must continue subgraph traversal.
-            nv->traverse(*node);
-
+            traverse(node,nv);
             
         }