bug#1727: 23.0.60; end-of-sentence and non-breaking space

[Chong Yidong]

>From bug#1726 and bug#1727:

> forward-sentence does not treat non-breaking space as a space for
> purposes of sentence ends.
...
> When I type C-x = at a non-breaking space, it tells me that it
> has code 160, hex a0.  But when I execute (insert "\xa0"),
> it inserts something that displays as `\240' and for which C-x =
> displays this:
>
>    Char:   (4194208, #o17777640, #x3fffa0, raw-byte) point=198 of 211
>    (93%) column=5
>
> Is that a bug?  It seems quite confusing to me.

ISTR that there was an extended discussion about classifying
non-breaking spaces on this list a while back.  But I can't find it now.
Does anyone remember the details?