bug#22581: Strange minibuffer prompt on exiting Emacs

[Eli Zaretskii <eliz@gnu.org>]

> From: Richard Copley <rcopley@gmail.com>
> Date: Sun, 7 Feb 2016 11:33:15 +0000
> 
> The prompt to confirm exiting Ediff has gone a bit strange. To
> reproduce in "emacs -Q" (assuming files "x" and "y" exist in the
> working directory):
> 
> M-x ediff RET x RET y RET q
> 
> The expected prompt is
> "Quit this Ediff session? (y or n)  ".
> 
> The actual text shown in the minibuffer is
> "Quit this Ediff session? (y or n)  switch-frame-".
> 
> (The frame switch event occurred because the little Ediff control
> panel frame went away and the main frame got activated.)
> 
> The "switch-frame-" is of course not really part of the prompt. It is
> rendered like what you get when you enter an incomplete key sequence,
> like "C-x-". It seems as though switch-frame is being treated as a
> prefix key, but it's not treated as such in most circumstances. Try
> this for example:
> 
> C-x 5 2 ;; make-frame-command
> C-h k ;; describe-key
> ;; Use the window manager to activate the other frame.
> ;; Minibuffer prompt is "Describe key (or click or menu item):  switch-frame-")
> RET
> ;; *Help* buffer describes "RET", not "switch-frame RET".

Stefan, could you please look into this?  AFAICS, this is caused by
your changes in 5dc644a to generalize the prefix-command machinery: a
binary built a day before that doesn't have this problem, while a
binary build 4 weeks later does.

Thanks.