bug#66379: 29.1.50; ediff wordwise ediff-copy-diff leads to different buffers

[Michael Heerdegen]

Felix Mühlenberend via "Bug reports for GNU Emacs, the Swiss army knife
of text editors" <bug-gnu-emacs@gnu.org> writes:

> Symptoms:
> Diffing the following regions with wordwise mode:
> ```[A]
> This, is a test
> ```
> ```[B]
> This is a test
> ```
> and copying with (ediff-copy-A-to-B) results in:
> ```[A]
> This, is a test
> ```
> ```[B]
> This ,is a test
> ```
> Where the comma is in the wrong place.

This is not the only case of such things happening.  The wordwise mode
is more or less whitespace agnostic, it doesn't care when copying
between the buffers.

AFAIR I did not have a good idea to fix this yet.  Of course one can
mess with the word classes to fix some special cases (but never all), I
even tried to make whitespace a separate class, but nothing ever worked
reliably.

Michael.