bug#12463: 24.2; pos-visible-in-window-p gets slower over time

[Eli Zaretskii]

> From: Chong Yidong <cyd@gnu.org>
> Date: Fri, 21 Sep 2012 11:52:42 +0800
> Cc: Jörg Walter <jwalt@garni.ch>, 12463@debbugs.gnu.org
> 
> Juanma Barranquero <lekktu@gmail.com> writes:
> 
> >> I have no idea what was originally supposed to ensure `image_types'
> >> doesn't include duplicate entries, so the patch may be way
> >> off... hope someone actually knows what is suppsed to go on there.
> >
> > What kind of duplicate entries image_types had? Were they mostly (or
> > all) for pbm/xbm types?
> 
> No, the duplicates were for other image types other than pbm/xbm (in
> this case svg).

Then how come the bug was triggered by having a pbm image in the
header line?