disallow slugs with spaces, and check POST for existing challenge
disallow slugs with spaces, and check POST for existing challenge

osmlab/maproulette,osmlab/maproulette,Crashfreak/maproulette,Crashfreak/maproulette,mvexel/maproulette,osmlab/maproulette,mvexel/maproulette,Crashfreak/maproulette,osmlab/maproulette,Crashfreak/maproulette,mvexel/maproulette,mvexel/maproulette