bug#57669: 29.0.50; C-n, C-p off under long lines

[Gregory Heytings]

> > > Commercial Emacs performs much worse
> >
> > I dunno.  As of 103caad, Commercial runs through the 100-line test in 
> > 3s, about the same as GNU with find-file-literally and non-nil 
> > long-lines-threshold.
>
> I'm aware of your "solution", and it is unacceptable.

I'm not, I asked him a few pointers, and he replied with the hash of a 
commit which disables what exists on master.  Perhaps there's something 
useful in his solution, even if it is unacceptable?  If you already know 
what it is, can you perhaps describe it in a few words?