Seems I can't "unforget" erroneously forgotten files, so will have to forget them and then re-add them
#ifndef BOOST_INTRUSIVE_PTR_HPP_INCLUDED
#define BOOST_INTRUSIVE_PTR_HPP_INCLUDED
//
// intrusive_ptr.hpp
//
// Copyright (c) 2001, 2002 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
//
// See http://www.boost.org/libs/smart_ptr/intrusive_ptr.html for documentation.
//
#include <boost/smart_ptr/intrusive_ptr.hpp>
#endif // #ifndef BOOST_INTRUSIVE_PTR_HPP_INCLUDED