bug#12911: 24.3.50; let users decide where (& perhaps whether) `emacs_backtrace.txt' files are written

[Eli Zaretskii]

> On 11/17/2012 07:58 PM, Eli Zaretskii wrote:
> > On Unix, the data winds up in some directory under user's home
> > directory.
> 
> No, on Unix that data is sent to the standard error stream.
> This is documented in the manual.

For the record, here's what the manual says:

  Emacs is not supposed to crash, but if it does, it produces a "crash
  report" prior to exiting.  The crash report is printed to the standard
  error stream.  If Emacs was started from a graphical desktop on a GNU
  or Unix system, the standard error stream is commonly redirected to a
  file such as `~/.xsession-errors', so you can look for the crash report
  there.  On MS-Windows, the crash report is written to a file named
  `emacs_backtrace.txt' in the current directory of the Emacs process, in
  addition to the standard error stream.

> It's common that stderr is redirected to a file,
> but it's also common that it's not.  Traditionally
> it's not, and many people commonly run Emacs that way.

Nowadays, tradition is shifting towards GUI invocation, so stderr will
be redirected more often than not.