bug#26650: 26.0.50; Protect *Backtrace* from accidental killing

[Tino Calancha <tino.calancha@gmail.com>]

On Tue, 25 Apr 2017, npostavs@users.sourceforge.net wrote:

> severity 26650 minor
> quit
>
> Tino Calancha <tino.calancha@gmail.com> writes:
>
>> (error "hi") ; This time kill *Backtrace*
>> C-x k RET
>>
>> ;; Eval it once more:
>> (error "hi")
>> ;; 'hi' is printed in echo area, but *Backtrace* is not shown.
>
> That's because you're still in the recursive edit, it's like evaluating
> '(error "hi")' before hitting 'q' in the *Backtrace* buffer.  You can
> use C-M-c (exit-recursive-edit) to get back to normal.  I think it would
> make sense to do that automatically if you kill the *Backtrace* buffer.
Yes, it would be useful.  I don't know how, though.
Sometimes i kill *Bactrace* from *Ibuffer*/*Buffer List* with the 
recursive edit still ongoing.  It's a classical mistake.