More random searches for factory locations

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7019 8aca7d54-2c30-db11-9de9-000461428c89
Lot of cleaned up factory buiulding code with more intelligent retrys and obeys the desired factry area for the next one

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7020 8aca7d54-2c30-db11-9de9-000461428c89