Warnings fixes for VS.

src/osgUtil/CullVisitor.cpp

@@ -84,6 +84,8 @@ class PrintVisitor : public NodeVisitor
         virtual void apply(LOD& node)           { apply((Group&)node); }
 
    protected:
+   
+        PrintVisitor& operator = (const PrintVisitor&) { return *this; }
     
         std::ostream& _out;
         int _indent;