sqapi: add player_x::is_active

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6332 8aca7d54-2c30-db11-9de9-000461428c89
sqapi: add world.remove_player

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6333 8aca7d54-2c30-db11-9de9-000461428c89
CODE cleanup of groundobj.*

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6334 8aca7d54-2c30-db11-9de9-000461428c89
FIX: stop vehicle smoke when convoy speed limited by way speed limit

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6335 8aca7d54-2c30-db11-9de9-000461428c89
FIX: factory goods recall with no_routing_over_overcrowded

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6336 8aca7d54-2c30-db11-9de9-000461428c89