CODE: improve squirrel error message

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7076 8aca7d54-2c30-db11-9de9-000461428c89
sqapi: add scenario.api to manage backward compatibility of scripts to the changing api

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7077 8aca7d54-2c30-db11-9de9-000461428c89