bug#13446: 24.2; Fix loop test in linum.el

[Stefan Monnier <monnier@iro.umontreal.ca>]

> not empty.)  Notice now that the margin for line numbers is three
> characters wide--large enough to hold "100", even though line 100 is not
> actually in the window.  This is caused by linum overlaying line 100,
> which it shouldn't be doing.  My patch fixes this.

Ah, got it!
Thank you, it makes perfect sense now,

BTW, in nlinum-mode, the default behavior is half-way between the two:
we don't try to accommodate the largest line number there can be
(partly to avoid scanning the whole buffer, which can be a performance
problem in itself), so we grow the margin only when we display a larger
number, but we don't shrink it back when moving back to the beginning of
the file with shorter line numbers.  The main reason was that I found it
annoying to have the margin grow&shrink all the time in those cases
where you're working right around line 100 or 1000.


        Stefan