Improve tests for new *_t template aliases.

Add missing *_t aliases.

doc/add_reference.qbk

@@ -18,6 +18,8 @@ for backwards compatibility only.
    {
       typedef __below type;
    };
+
+   template <class T> using add_reference_t = typename add_reference<T>::type; // C++11 and above
   
 __type If `T` is not a reference type then `T&`, otherwise `T`.
 

doc/type_identity.qbk

@@ -12,6 +12,8 @@
    {
       typedef T type;
    };
+
+   template <class T> using type_identity_t = typename type_identity<T>::type; // C++11 and above
   
 __header ` #include <boost/type_traits/type_identity.hpp>` or ` #include <boost/type_traits.hpp>`