Hello.

I sometimes use linum-mode, then I meet a problem.
It is displaying a wrong line number when there is an invisible line.
(I don't know the problem is a bug clearly, but it is trouble to me.)

    Example:
    ====================================================================
      In buffer (linum-mode is enabled).

        1 abc
        2 def
        3 ghi
        4 jkl

      Make the 2nd line ("def\n") invisible (by `facemenu-set-invisible').

        1 abc
        2 ghi                   <= wrong
        4 jkl
    ====================================================================

I fixed the problem.

    the attached file: "linum-mode.el.1.diff"
                       (based on Emacs 23.3.)

(If the following additional improvement is unnecessary, please ignore.)

Additionally, I improved about invisible buffer string.

    the attached file: "linum-mode.el.2.diff"
                       (including the above bug fix.)

  (1) Indicating invisible line(s) by an underlined line number
      when the following line(s) is/are invisible.

    ====================================================================
        _1_ abc                 <= underline
         3  ghi
         4  jkl
    ====================================================================

  (2) Indicating partial invisible string by a `strike-through' line
      number when the line has partial invisible string.

    ====================================================================
        _1_ abc
         3  ghi
         4  jkl

      Make the 3rd line ("hi") invisible partially.

        _1_ abc
        -3- g                   <= strike-through
         4  jkl

      Make the 1st line ("ab") invisible partially.

        -_1_- c                 <= underline and strike-through
         -3-  g
          4   jkl
    ====================================================================

  For the additional improvement,
check the new variable `linum-indicate-invis',
and eval the following, please.

    (setq linum-indicate-invis t)