bug#1806: dired-pop-to-buffer in wrong place

[martin rudalics]

> I think either behavior is acceptable as long as it can be overridden by
> the user (via special-display-buffer-names).  Reproducing the previous
> behavior (of ignoring pop-up-frames) is probably the safer option, and
> it at least would suit my use-pattern better as well (I do have
> pop-up-frames set to t but would rather not have a new frame created for
> those dired-lists unless I explicitly set one up in
> special-display-buffer-names with a specific geometry).

Maybe we should have `special-display-popup-frame' handle yet another
phony parameter, say 'split-window, making it split the selected window
if that is set.

martin