Save 752 image indecies for ground

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6971 8aca7d54-2c30-db11-9de9-000461428c89
FIX: two other errors with bridgebuilder

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6972 8aca7d54-2c30-db11-9de9-000461428c89