Fix ToString for std classes.

env/message_list.hpp

@@ -1,13 +1,12 @@
 #pragma once
 
 #include "strings.hpp"
-
+#include "message_std.hpp"
 
 namespace msg
 {
 
 inline string ToString(char const * s) { return s; }
-inline string ToString(string const & s) { return s; }
 
 /// Override ToString function for your custom class in it's namespace.
 /// Your function will be called according to the ADL lookup.

env/message_std.hpp

@@ -4,9 +4,11 @@
 #include "../std/sstream.hpp"
 
 
-namespace msg
+namespace std
 {
 
+inline string ToString(string const & s) { return s; }
+
 template <class T> string ToString(vector<T> const & v)
 {
   ostringstream ss;