bug#21598: 24.5; Auto-revert-mode loads images as text

[Eli Zaretskii]

> From: Matthias Redies <rediesmatthias@yahoo.de>
> Date: Thu, 1 Oct 2015 17:17:03 +0200
> 
> 1. open image C-x C-f and select "output.png". This will display the 
> image as an image as it should.
> 2. change Image using an external program. This causes the
> auto-revert-mode to reload the image(good), but as a text, although my
> default (as in 1.) is to open the picture as an image

This happens because autorevert.el calls revert-buffer with its 3rd
argument non-nil.  It is easy to change that to nil for buffers under
image-mode, but I'm curious why doesn't autorevert.el do that for all
the other modes.  Does anyone know?