New API in libxml++ 3.2

Member xmlpp::Document::process_xinclude (bool generate_xinclude_nodes, bool fixup_base_uris)
Member xmlpp::DomParser::get_xinclude_options (bool& process_xinclude, bool& generate_xinclude_nodes, bool& fixup_base_uris) const noexcept
Member xmlpp::DomParser::set_xinclude_options (bool process_xinclude=true, bool generate_xinclude_nodes=true, bool fixup_base_uris=true) noexcept