CORBA24 — POA status during destruction is unclear

The description of POA destroy in section 11.3.8.4 is unclear.
There are several ways to implement this, which may result in problems
porting application code between orbs.

Some of the ambiguities are:

1) It may or may not be legal for an application to create new child POAs
while the existing children are being destroyed. This could happen
explicitly or via AdapterActivators. Such behavior could prevent destruction
from ever completing.

2) If the POA's POAManager is in the holding state at the time of
destruction (or if its state is changed to holding during the destruction
process), it isn't clear what happens to the held requests.

3) If the POA's POAManager is active, what happens to requests that arrive
after the call to destroy but before the destruction becomes apparent? If
they are to be serviced, a sufficiently rapid arrival rate may prevent the
destruction from ever completing.

Clarify POA behavior during destruction as described below