fix linking with clang

boost::optional<std::string> destructor was not generated
do not index (for autocomplete) way without city associated

fix http://jira.canaltp.fr/browse/NAVITIAII-1359
-warning clang
Merge pull request #747 from TeXitoi/do-not-index-way-without-admin8

Do not index (for autocomplete) way without city associated