bug#50946: insert-file-contents can corrupt buffers.

[Eli Zaretskii]

> Date: Sun, 3 Oct 2021 17:21:35 +0000
> Cc: joaotavora@gmail.com, 50946@debbugs.gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> > So the text you propose is too "frightening", in that it basically
> > says "don't use that".  Which is too tough, because valid use cases to
> > use that feature do exist, and if the programmer knows what he/she is
> > doing it doesn't have to produce garbled buffers.  For the manual, we
> > need more informative text, which mentions coding-system-for-read.
> 
> OK, how about this third version of my patch?

LGTM, thanks.