Use a local copy of is_same trait.

boost::core::is_same is deprecated, so use a local copy to avoid adding
a dependency on Boost.TypeTraits. Use Boost.TypeTraits in tests.

Also added a missing include.

include/boost/bind/detail/is_same.hpp

@@ -0,0 +1,36 @@
+#ifndef BOOST_BIND_DETAIL_IS_SAME_HPP_INCLUDED
+#define BOOST_BIND_DETAIL_IS_SAME_HPP_INCLUDED
+
+// is_same<T1,T2>::value is true when T1 == T2
+//
+// Copyright 2014 Peter Dimov
+//
+// Distributed under the Boost Software License, Version 1.0.
+// See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/config.hpp>
+
+#if defined(BOOST_HAS_PRAGMA_ONCE)
+# pragma once
+#endif
+
+namespace boost
+{
+namespace _bi
+{
+
+template< class T1, class T2 > struct is_same
+{
+    BOOST_STATIC_CONSTANT( bool, value = false );
+};
+
+template< class T > struct is_same< T, T >
+{
+    BOOST_STATIC_CONSTANT( bool, value = true );
+};
+
+} // namespace _bi
+} // namespace boost
+
+#endif // #ifndef BOOST_BIND_DETAIL_IS_SAME_HPP_INCLUDED

include/boost/bind/detail/result_traits.hpp

@@ -22,6 +22,7 @@
 //
 
 #include <boost/config.hpp>
+#include <boost/core/ref.hpp>
 
 #if BOOST_CXX_VERSION >= 201700L
 #include <functional>