CORBA24 — ORB::shutdown underspecified

If I call ORB::shutdown(), it implicitly calls POA::destroy() on the
Root POA.

I assume that the value of the wait_for_completion parameter to
ORB::shutdown() should be passed through to POA::destroy()? The spec isn't
entirely clear on this point.

Further, what is the effect of calling ORB::shutdown() on the value
of the etherealize_objects parameter for POA::destroy()? Since ORB::shutdown()
doesn't have an etherealize_objects parameter itself, the value passed
through to POA::destroy must be implicit, but the spec doesn't say what
it is.

Similarly, ORB::destroy() implicitly calls ORB::shutdown(). From the
second-last para on page 4-35, it would appear that this implicit call
is made as ORB::shutdown(true) rather than ORB::shutdown(false). It
might be nice to make this explicit so I don't have to read between the
lines to figure it out.

Incorporate changes and close issue.