bug#743: 23.0.60; linum-mode margin display wrong

[Chong Yidong]

Hi Markus,

Could you try to debug this?  I'm not sure if it's a linum.el bug or a
redisplay bug.

> $ emacs -Q -eval '(progn (linum-mode 1) (insert-char ?\n 100) (goto-line 12) 
> (redisplay) (kill-line 10))'
>
> The numbering in the margin of the first lines looks like:
>
>   |
>   |
>   |
>   |
>   |
>   |
>   |
>   |
>   |
>  1|
>  1|
>  1|
> 13|
> 14|
> ...
>
> The first 12 lines have a display margin string that is 3 characters
> long (space padded), but the margin is only 2 columns wide, so the last
> digit is lost.