bug#8865: 24.0.50; `display-buffer' does not respect `pop-up-frames'

[Drew Adams]

> > My question was about replacing such a test.  The common 
> > denominator of the intentions behind using such tests is
> > what all of those tests do (have in common): distinguish
> > nil `pop-up-frames' from non-nil.  Nothing more.
> 
> If that's all you want to do, then "(if pop-up-frames" is (trivially)
> the only answer.

Well, yes, in Emacs 20-23.  But if `pop-up-frames' is being deprecated then what
is the _replacement_ for such a test, going forward?