FIX: if cross_connect_factories is on clear supplier array during load

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6306 8aca7d54-2c30-db11-9de9-000461428c89
FIX: winter snowline can be set to negative values too

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6307 8aca7d54-2c30-db11-9de9-000461428c89