bug#10873: 24.0.93; `report-emacs-bug' obscures bug-reporting buffer (!)

[martin rudalics <rudalics@gmx.at>]

 >> This bug is still 100% reproducible in an Emacs 25 build of 2015-12-10:
 >
 > Martin, could you please look into this?

There's not much I can do about this.  I can give a simpler recipe with
emacs -Q: Type C-h f set- RET and see the *Completions* window pop up.
Then type M-x report-emacs-bug.

OT1H the window showing the *Completions* buffer is softly dedicated to
that buffer.  This is necessary to make sure that an intermittent
‘display-buffer’ does not steal that window for showing another buffer.
Windows showing *Completions* should disappear immediately when they are
no more needed but till then they should be continuously visible.

OTOH ‘report-emacs-bug’ apparently assumes that it always has two
windows at its disposal - one for the message and one for help.  This
assumption misfires with the recipe at hand.  (Note that my machine in
addition also displays a warning from ‘compose-mail’ which gets usually
immediately buried when showing either the message or the help.)

IMO this report is the result of a cockpit error.  As long as a "modal"
window like that showing *Completions* is open, users should not start
an unrelated activity, including that of writing a bug report.

If, however, people think that ‘report-emacs-bug’ should always succeed
showing both of its windows in every conceivable context, we can do that
easily by calling ‘delete-other-windows’ before ‘display-buffer’.  This
will clearly misfire for people showing more than two windows per frame.

So it's your choice ...

martin