Do not switch focus to the completions buffer window

[Leo Alekseyev]

Hi all,
How would I go about preventing *Completions* buffer window from receiving
focus?  I find some value in having it pop-up, but its usability is very
questionable.  Using Tomohiro Matsuyama's popwin, it is very easy to
dismiss the buffer with C-g.  What I want is for it not to even receive
focus.  I tried creating the following piece of advice; the code doesn't
work but it gives you an idea of what I'm after:

(defadvice comint-dynamic-list-filename-completions (around
unfocus-completions-buffer activate)
  (let ((cur-win (selected-window)))
    ad-do-it
    (select-window cur-win)))


Thanks,
--Leo