Move placeholders to namespace boost::placeholders.

include/boost/bind.hpp

@@ -10,7 +10,7 @@
 //
 //  bind.hpp - binds function objects to arguments
 //
-//  Copyright (c) 2009 Peter Dimov
+//  Copyright (c) 2009, 2015 Peter Dimov
 //
 //  Distributed under the Boost Software License, Version 1.0.
 //  See accompanying file LICENSE_1_0.txt or copy at
@@ -21,4 +21,6 @@
 
 #include <boost/bind/bind.hpp>
 
+using namespace boost::placeholders;
+
 #endif // #ifndef BOOST_BIND_HPP_INCLUDED