FIX: properly mark old top window dirty if new window gets on top

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7167 8aca7d54-2c30-db11-9de9-000461428c89
FIX: halt and convoy info window with large theme

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7168 8aca7d54-2c30-db11-9de9-000461428c89