--- enclosed?           ruby 1.8 feature

    enclose ξ֤򿿵֤ͤޤ
    freeze 줿 ThreadGroup  Thread ɲ/ϤǤʤʤޤ
    enclosed?  false ֤ޤ

        thg = ThreadGroup.new
        p thg.enclosed?         # => false
        thg.enclose
        p thg.enclosed?         # => true

        thg = ThreadGroup.new
        p thg.enclosed?         # => false
        thg.freeze
        p thg.enclosed?         # => false

