bug#20674: linum-mode overwrites existing margin width

[Eli Zaretskii]

> From: "Paul W. Rankin" <hello@paulwrankin.com>
> Date: Wed, 27 May 2015 17:56:03 +1000
> 
> I set the window left margin to 25 columns, then activated linum-mode,
> which sets the left margin to 3 columns (to accommodate the number of
> figures in the total line numbers).
> 
> Expected behaviour:
> 
> linum-mode should only expand left margin as needed, not
> overwrite/shrink it.

I think linum-mode is incompatible with any other means of putting
anything inside the display margins, because it actually writes
there.  The width of the margin is just the tip of the iceberg,
because at best you will have margins whose contents are overwritten
by linum-mode.