Improve visibility of concept failure messages

[SVN r47793]

include/boost/concept/detail/general.hpp

@@ -29,6 +29,16 @@ struct requirement
     static void failed() { ((Model*)0)->~Model(); }
 };
 
+struct failed {};
+
+# ifndef BOOST_NO_PARTIAL_SPECIALIZATION
+template <class Model>
+struct requirement<failed ************ Model::************>
+{
+    static void failed() { ((Model*)0)->~Model(); }
+};
+# endif
+
 # ifdef BOOST_OLD_CONCEPT_SUPPORT
 
 template <class Model>
@@ -42,17 +52,28 @@ struct requirement_<void(*)(Model)>
   : mpl::if_<
         concept::not_satisfied<Model>
       , constraint<Model>
+# ifndef BOOST_NO_PARTIAL_SPECIALIZATION
+      , requirement<failed ************ Model::************>
+# else
       , requirement<Model>
+# endif 
     >::type
 {};
   
 # else
 
 // For GCC-2.x, these can't have exactly the same name
+# ifndef BOOST_NO_PARTIAL_SPECIALIZATION
 template <class Model>
 struct requirement_<void(*)(Model)>
-  : requirement<Model>
+    : requirement<failed ************ Model::************>
 {};
+# else
+template <class Model>
+struct requirement_<void(*)(Model)>
+    : requirement<Model>
+{};
+# endif 
   
 # endif