FIX: loading of old tunnels again

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6725 8aca7d54-2c30-db11-9de9-000461428c89
FIX: take speed limtis into account for choose signals searches

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6726 8aca7d54-2c30-db11-9de9-000461428c89