remove forward declaration

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7402 8aca7d54-2c30-db11-9de9-000461428c89
sqapi: add operators to coord classes, conversion to string

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7403 8aca7d54-2c30-db11-9de9-000461428c89