extend FT to check that stones played on one board don't appear on another
extend FT to check that stones played on one board don't appear on another

karlorg/drunken-octo-avenger,karlorg/drunken-octo-avenger,allanderek/drunken-octo-avenger,allanderek/drunken-octo-avenger,allanderek/drunken-octo-avenger,allanderek/drunken-octo-avenger,karlorg/drunken-octo-avenger,karlorg/drunken-octo-avenger