--- rstrip    ruby 1.7 feature
--- rstrip!   ruby 1.7 feature

    ʸˤʸƼޤ
    ʸ " \t\r\n\f\v" Ǥ

    rstrip ϲùʸ򿷤֤ޤ

    rstrip! ϼȤѹ֤ޤ
    򤬤ʤäȤ nil ֤ޤ

        p " abc\n".rstrip        #=> " abc"
        p " abc \t\r\n".rstrip   #=> " abc"
        p " abc".rstrip          #=> " abc"

        str = "abc\n"
        p str.rstrip           #=> "abc"
        p str                  #=> "abc\n"  (Ѳʤ)

        str = "abc  "
        p str.rstrip!          #=> "abc"
        p str                  #=> "abc"  (Ѳ)

        str = "abc"
        p str.rstrip!          #=> nil
        p str                  #=> "abc"

    ruby 1.8 feature:  "\0" ޤФơ
    lstrip  "\0" ̰ޤ

        str = "abc  \0"
        p str.rstrip           # => "abc"

