--- Dir.new(path)
--- Dir.open(path)
--- Dir.open(path) {|dir| ...}

    pathФǥ쥯ȥꥹȥ꡼򥪡ץ󤷤֤ޤ
    ץ˼Ԥ㳰 Errno::EXXX ȯޤ

    open()ϥ֥åꤹ뤳ȤǤޤ
    ֥åꤷƸƤӽФϡǥ쥯ȥꥹȥ꡼
    Ϳƥ֥å¹Ԥޤ֥åμ¹Ԥλȡ
    ǥ쥯ȥϼưŪ˥ޤ

    ruby 1.7 feature:
    ֥åꤵ줿ȤΤΥ᥽åɤͤϥ֥åμ¹Է
    Ǥ

