Unsplittable window question.

[Ergus]

Hi:

I am experimenting with some off the windows/frame features. And I added
these two lines to my config:

```
(defconst my/display-buffer-at-bottom
  '((display-buffer-reuse-window display-buffer-at-bottom)
      (unsplittable . t)
      (dedicated . t)
      (window-height . 0.3)))

(add-to-list 'display-buffer-alist `("*Occur*" . ,my/display-buffer-at-bottom))
```

With this Occur opens in the bottom as expected, but the
(unsplittable . t) seems not to have any effect. Emacs splits the Occur
window like any other and:

(window-parameter (get-buffer-window "*Occur*") 'unsplittable)

returns nil.

The debugger shows the call to display-buffer-at-bottom passing the
alist as a parameter.

What I am doing wrong?

Thanks in advance,
Ergus