More warning suppression

[SVN r20996]

include/boost/iterator/iterator_concepts.hpp

@@ -72,6 +72,7 @@ namespace boost_concepts {
       value_type v = r;
       value_type v2 = *i;
       boost::ignore_unused_variable_warning(v);
+      boost::ignore_unused_variable_warning(v2);
     }
     Iterator i;
   };