bug#15961: 24.3.50; display-buffer-at-bottom not at bottom

[martin rudalics]

>> If I bind `split-width-threshold' in `display-buffer-at-bottom', the
>> user won't be able to override it either.
>
> Of course, she can, because she can set her display-buffer-alist such
> that she doesn't go through display-buffer-at-bottom but through another
> function of her own choosing instead.

So the only viable choice is to not set `split-width-threshold' anywhere
and tell the user that if she wants a window below via
`display-buffer-at-bottom' she has to customize `split-width-threshold'.

martin