squelch unused-variable compiler warnings

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7301 8aca7d54-2c30-db11-9de9-000461428c89
FIX: mark ticker dirty when it gets cleared

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7302 8aca7d54-2c30-db11-9de9-000461428c89