bug#17234: 24.3.50; overlay priority : cons cells make an error in ediff

[Glenn Morris]

Stefan Monnier wrote:

>> But I imagine ediff was not the only package trying to get the priority
>> of an overlay and do something with the answer (however misguided you
>> think that might be).
>
> Hard to tell.

One minute of searching suggests that:

extent-at in lucid.el
ps-generate-postscript-with-faces1 in ps-def.el

will have problems now.

It would seem suprising if there are three files in Emacs that this
causes problems for, and nothing external.

> Not sure what we can do about it, tho.

The least you can do is make an "incompatible change" NEWS entry.
Ideally it would it explain what do if you still want to get the
priority of an overlay as a number.