bug#25295: Represent eieio objects using object-print in backtraces and edebug

[Stefan Monnier]

>> And I'll stop thinking about interaction with concurrency.
> There should be none, since only one thread running Lisp could be
> doing that at any given time.  Right?

I'm thinking of

   prin1
   -> enters print.c
   -> calls back the custom Elisp-side object-print
   -> which decides to accept-process-output


-- Stefan