The shared memory is explicitly destroyed by `tao_shared_object_detach`.
Handling of the `TAO_PERSISTENT` bit is done at the shared object level,
not shared memory level.  The same mechanism works for Linux and Mac-OSX.
Another consequence is that TAO shared objects not properly detached will
be persistent.  This is useful for debugging.  Use `ipcs` and `ipcrm -m`
to list and remove such objects.