bug#24169: 25.1.50; Line numbers disappear when horizontally scrolled

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Date: Sat, 6 Aug 2016 13:52:06 -0400
> Cc: ivan <ivan.brennan@gmail.com>, 24169@debbugs.gnu.org
> 
> Wouldn't it be simpler to put the overlay over the whole line, so it
> doesn't need to be moved?

How do you do that, given that display in the margins is a "replacing"
display: it is done _instead_ of the text covered by the property?
Linum-mode uses a before-string to avoid losing buffer text due to
that, and I don't see how you would do that "over the whole line".  Am
I missing something?