CODE: compute connected components and use them in route search

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6316 8aca7d54-2c30-db11-9de9-000461428c89
CODE: simplify and slightly optimize factory_bauplatz_mit_strasse_sucher_t

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6317 8aca7d54-2c30-db11-9de9-000461428c89