CODE: calc_current_speed does not call karte_t::lookup anymore

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6879 8aca7d54-2c30-db11-9de9-000461428c89
CODE: get rid of unnecessary get_2d() calls

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6880 8aca7d54-2c30-db11-9de9-000461428c89
ADD: Dispaly fix vehcile cost in convoi details

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6881 8aca7d54-2c30-db11-9de9-000461428c89