Merge pull request #191 from boostorg/adapt-adt/return-const

adapt/adt: Don't add/remove const on return type of attributes

test/sequence/adapt_adt.cpp

@@ -302,7 +302,7 @@ main()
         BOOST_MPL_ASSERT((
             boost::is_same<
                 boost::fusion::result_of::back<ns::point const>::type::type,
-                const int
+                int
             >));
     }