Seems I can't "unforget" erroneously forgotten files, so will have to forget them and then re-add them
#ifndef BOOST_MPL_PLUS_HPP_INCLUDED
#define BOOST_MPL_PLUS_HPP_INCLUDED
// Copyright Aleksey Gurtovoy 2000-2004
//
// 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)
//
// See http://www.boost.org/libs/mpl for documentation.
// $Id: plus.hpp 49267 2008-10-11 06:19:02Z agurtovoy $
// $Date: 2008-10-11 02:19:02 -0400 (Sat, 11 Oct 2008) $
// $Revision: 49267 $
#define AUX778076_OP_NAME plus
#define AUX778076_OP_TOKEN +
#include <boost/mpl/aux_/arithmetic_op.hpp>
#endif // BOOST_MPL_PLUS_HPP_INCLUDED