bug#69983: Use category for display-buffer-alist

[martin rudalics]

>> But if so, you should say that this works only
>> when called from 'display-buffer'.
>
> This already says so:
...
> +  * `category': the buffer matches a category as a symbol if
> +    the caller of `display-buffer' provides `(category . symbol)'
> +    in its action argument.
...

I was never really fond of using 'buffer-match-p' for 'display-buffer'.
This is an example why.  A caller of 'buffer-match-p' who does not know
about 'display-buffer' has to care about whether the CONDITION passed to
it contains a 'category' element.

martin