the hook - the hook only needs the Atom to control access to the selection
object. Upgraded the SelectionCallback to take a client argument and
additional type codes so that it can be used for redirection.
delivery of events to windows and clients.
This is tentative. It's likely that an additional last-resort hook will
be necessary for code that calls TryClientEvents or WriteEventsToClient
directly. It's also possible that new xace machinery will be necessary
to classify events and pull useful resource ID's out of them.
The failure case also needs some thinking through. Should event delivery
"succeed" or should it report undeliverable?
Finally, XKB appears to call WriteToClient to pass events. Sigh.
arbitrary X status codes instead of just TRUE/FALSE.
The dix layer in most cases still does not propagate the return value of
XACE hooks back to the client, however. There is more error propagation
work to do.