--- SystemCallError === other  ruby 1.7 feature

    other  SystemCallError Υ֥饹ǤпǤ
    (Module#=== [Module/===] Ʊ)

    ޤդ SystemCallError Υ֥饹Ǥ硢
    other.errno (nil ʤ Υ饹
    Errno [Errno::EXXX/Errno] ) 
    self::Errno Ʊ˿֤ޤ

    Υ᥽åɤˤꡢƥˤä errno Ʊͤ㳰Ф
    ʲΤ褦ªǤ褦ˤʤäƤ((**))

        p Errno::EAGAIN::Errno
        p Errno::EWOULDBLOCK::Errno
        begin
          raise Errno::EAGAIN, "pseudo error"
        rescue Errno::EWOULDBLOCK
          p $!
        end

        # => 11
             11
             #<Errno::EAGAIN: pseudo error>

    ߡ SystemCallError#=== Τħä˰̣ޤ
    (ʲΤ褦ƱΥ֥ȤˤʤäƤ뤫Ǥ)

        p Errno::EAGAIN
        p Errno::EWOULDBLOCK
        p Errno::EWOULDBLOCK.id
        p SystemCallError.new(11).class.id

        => Errno::EAGAIN
           Errno::EAGAIN
           537747360
           537747360

