rem: bool operator<(boost::filesystem::path const& lhs , boost::filesystem::path const& rhs) { return lhs.string() < rhs.string(); }
add: bool operator<(file_key const& fk) const { if (info_hash < fk.info_hash) return true; if (fk.info_hash < info_hash) return false; return file_path < fk.file_path; }
context: bool operator<(boost::filesystem::path const& lhs	, boost::filesystem::path const& rhs){	return lhs.string() < rhs.string();}