bug#22299: Obsolete selective-display

[Stefan Monnier]

>> The second one is a UI functionality and it's sufficiently "not terribly
>> useful" that nobody bothered to write a replacement for it using
>> overlays (instead, all the possible replacements provide a more tailored
>> functionality).
> Right.  So if we don't want to obsolete the other form (and Eli says he
> uses it all the time, so it doesn't sound like we want to), then I guess
> there's nothing more to be done here?  So I'm closing this bug report.

We could try and re-implement `set-selective-display` using overlays,
of course.

And we could try and provide some other "text hiding" package more
specifically tailored to Eli's uses.

But really, I don't mind the `set-selective-display` feature now how
it's currently implemented, so I don't see a strong need to
replace/obsolete it.

The "selective-display == t" case is the one I care about because it
causes (well, "caused" since we started to drop that kind of
compatibility code) complexity in packages which had to deal with "end
of line can also be \r".


        Stefan