CODE: remove unused routines in ribi.h

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6965 8aca7d54-2c30-db11-9de9-000461428c89
FIX: tunnel building works correctly with (possibly double) underground slopes

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6966 8aca7d54-2c30-db11-9de9-000461428c89
FIX signal direction of last signal when dragging

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6967 8aca7d54-2c30-db11-9de9-000461428c89