bug#25295: 26.0.50; Represent eieio objects using object-print in backtraces and edebug

[Eric Abrahamsen]

EIEIO class instances can either be represented using the read-only
#<class-name object string> style, or as vectors, dumping all the slot
information. For large or recursive objects, this can take some time, and
can also make for very large strings. In backtraces and edebug, in
particular, this can make it very difficult to see what's happening.

Objects have an `object-print' method which produces the #<foo>
representation, but this appears to only sometimes be used in edebug,
and never in backtraces.

It would be great if object-print could always be used, or if there were
an option to toggle this.

In GNU Emacs 26.0.50.9 (x86_64-unknown-linux-gnu, GTK+ Version 3.22.5)
 of 2016-12-26 built on clem
Repository revision: 65b997b95e284e2edc1266663e39791f68d76ad7
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
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