Virtual frame-grabber and shared camera now provide information about the list
of shared arrays created by the virtual frame-grabber.  This is to imporve
efficiency of clients which no longer need to systematically attach posted
images.  It has also been clarified that the `counter` member in shared arrays,
in virtual frame-grabber structure and shared cameras reflects the number of
images posted by the virtual frame-grabber.  Then the index of the shared array
in the list is given by:

    index = (counter - 1)%length

where `length` is the length of the list and providing `counter > 0`.

A number of members in TAO structures have been qualified as `volatile` (those
which may atomically change) or as `const` (those which are immutable).