CORBA23 — Local operations on CORBA::Object

Summary: Basically, people get confused about which operations on CORBA::Object
can go remote. It"s clear from the GIOP spec that only non_existent(),
is_a(), get_interface(), and get_domain_managers() can go on the wire.
It follows that things like nil(), hash(), and is_equivalent() must be
local. However, as Owen Rees pointed out, this only applies to GIOP, not
the core, but a compliant ORB need not provide GIOP.

It seems that it would be a good idea to add some clarification to the core
to state which operations on CORBA::Object must be local and which ones
may (but need not) go remote.

Incorporate changes in 2.4 and close issue