FIX: AI should not try to start tunnels/bridges at planned tunnel/bridge end

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6320 8aca7d54-2c30-db11-9de9-000461428c89
FIX: AI player should check for water tile when creating ship schedule

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6321 8aca7d54-2c30-db11-9de9-000461428c89