Fix generic_stringize example compilation on Darvin (refs #9046)

[SVN r85868]

example/generic_stringize.cpp

@@ -17,9 +17,8 @@
 */
 
 #include <boost/lexical_cast.hpp>
-#include <boost/noncopyable.hpp>
 
-struct stringize_functor: boost::noncopyable {
+struct stringize_functor {
 private:
     std::string& result;