bug#28978: 26.0; Regression: separate, dedicated `*Completions*' frame no longer has parameter `minibuffer'

[martin rudalics <rudalics@gmx.at>]

 > The problem is that (1) PREVIOUSLY, frame *Completions*
 > had a nil `minibuffer' and (2) NOW, frame *Completions*
 > has a `minibuffer' parameter whose value is the active
 > minibuffer window (on the minibuffer frame).
 >
 > Does the problem description make more sense now?
 > Sorry for the confusion.

It does so indeed.  The change and its motivation are:

	Fix semantics of 'minibuffer' frame parameter

	The 'minibuffer' frame parameter is now t for a normal frame
	(a frame with a root window plus a minibuffer window) and the
	frame's minibuffer window for a minibuffer-less frame (a frame
	whose minibuffer window is on another frame).  See also:
	https://lists.gnu.org/archive/html/emacs-devel/2016-07/msg01259.html

	* src/frame.c (make_frame, make_frame_without_minibuffer)
	(make_minibuffer_frame): When assigning the frame's minibuffer
	window also store corresponding 'minibuffer' frame parameter.
	(store_frame_param): Move the 'minibuffer' parameter checks to
	the beginning so we can silently override the value before it
	gets stored in the parameter alist.  Fix error handling.
	(Fframe_parameters): Return value of 'minibuffer' parameter
	unmodified.

	* lisp/frameset.el (frameset-filter-minibuffer): When the cdr of
	the parameter is a minibuffer window, save (minibuffer . nil)
	instead of (minibuffer . t).
	(frameset--reuse-frame): To find a non-minibuffer-only frame
	look out for a frame whose 'minibuffer' parameter is t instead
	of that frame's minibuffer window.
	(frameset-minibufferless-first-p): To find a minibuffer-less
	frame look out for a frame whose 'minibuffer' parameter is a
	window instead of nil.

martin