Define traits::is_view for non fusion types

include/boost/fusion/support/is_view.hpp

@@ -14,6 +14,7 @@
 namespace boost { namespace fusion
 {
     // Special tags:
+    struct non_fusion_tag;
     struct sequence_facade_tag;
     struct boost_tuple_tag; // boost::tuples::tuple tag
     struct boost_array_tag; // boost::array tag
@@ -32,6 +33,13 @@ namespace boost { namespace fusion
             };
         };
 
+        template <>
+        struct is_view_impl<non_fusion_tag>
+        {
+            template <typename T>
+            struct apply : mpl::false_ {};
+        };
+
         template <>
         struct is_view_impl<sequence_facade_tag>
         {