--- lstrip    ruby 1.7 feature
--- lstrip!   ruby 1.7 feature

    ʸƬˤʸƼޤ
    ʸ " \t\r\n\f\v" Ǥ

    lstrip ϲùʸ򿷤֤ޤ

    lstrip!  self ѹ֤ޤ
    򤬤ʤäȤ nil ֤ޤ

        p "  abc\n".lstrip     #=> "abc\n"
        p "\t abc\n".lstrip    #=> "abc\n"
        p "abc\n".lstrip       #=> "abc\n"

        str = "\nabc"
        p str.lstrip           #=> "abc"
        p str                  #=> "\nabc"  (Ѳʤ)

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

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

