--- all?
--- all? {|item| ... }

    ruby 1.7 feature:

    ٤ƤǤǤ true ֤ޤǤǤ
    С false ֤ޤ

    ruby 1.8 feature:
    ֥åȼϡǤФƥ֥åɾ٤Ƥη
    Ǥ true ֤ޤ֥å֤ǡ
     false ֤ޤ

        p [1,2,3].all? {|v| v > 0}   # => true
        p [1,2,3].all? {|v| v > 1}   # => false

