bug#22009: PATCH: Use `window-total-width' in `window-splittable-p'

[martin rudalics]

> Yes, thanks.  But that still doesn't suggest how to fix
> window-splittable-p, unless we care _only_ for Joost's use case.  And
> I don't think we can declare that only such use cases matter, as
> window-splittable-p is too general-purpose for that.

Indeed.  Joost's fix also takes care of fringes, scroll bars and
dividers.

> We agree that the code should be fixed.  We just disagree about (or
> don't know) _how_ to fix it.

If we do not fix the code on the release branch I have to fix a couple
of doc-strings there telling that for historical reasons we do compare
apples and oranges.  Affected are ‘window-splittable-p’,
‘split-window-sensibly’ and ‘split-width-threshold’.  For the latter two
I'd have to amend the Elisp manual as well.

martin