bug#16619: 24.3.50; REGRESSION: transparent *Completions* now

[Drew Adams <drew.adams@oracle.com>]

It's even worse than what I reported at first.

Other special-display frames that pop up when the minibuffer is
active are also transparent.  This includes frame *Pp Eval Output*
if I do `M-:' while the minibuffer is active (e.g., from `M-x').  

(I have `M-:' bound in minibuffer maps to a command that essentially
does pp-eval-expression, and *Pp Eval Output* is a special-display
buffer because of `special-display-regexps'.)

And it includes frame *Backtrace* if I try to use the debugger
when the minibuffer is active.

However, I discovered something else that might help you solve
this mystery.  In all cases where I get a transparent frame
popped up, the frame that was selected when I invoked a command
that used the minibuffer was an ordinary frame, not my standalone
minibuffer frame.

If I instead first select the minibuffer frame (which is useless
for normal use, but worthwhile for this experiment) and I then
invoke a command (such as `M-x') from there that activates the
minibuffer, then *Completions* is normal - not transparent.

So something in this build is acting normal only when the
standalone minibuffer frame is selected before minibuffer
activation, and popping up transparent frames when another frame
is selected before minibuffer activation.