core/is_value and value. Identify val() at run time

include/boost/phoenix/core/is_value.hpp

@@ -45,12 +45,13 @@ namespace boost { namespace phoenix
         : is_value<T>
     {};
 
+    // This does not seem to work.
+    // There is an alternative in value.hpp which does work.
     template <typename T>
     struct is_value< expression::value<T> >
         : mpl::true_
     {};
 
-
     template <typename T>
     bool is_val(T const &t)
     {

include/boost/phoenix/core/value.hpp

@@ -52,6 +52,12 @@ namespace boost { namespace phoenix
         return expression::value<T>::make(t);
     }
 
+    // Identifies this Expr as a value.
+    template <typename Expr>
+    struct is_value<actor<Expr>  >
+        : mpl::true_
+    {};
+
     // Call out actor for special handling
     template<typename Expr>
     struct is_custom_terminal<actor<Expr> >