[OpenAFS] user-visible change suggestion for fs setacl

[Derrick J Brashear]

The provided patch adds the ability to add or subtract rights from an acl 
element, e.g. a+ or a- to add or subtract the administer bit from an acl, 
like fs sa . shadow a+
would give shadow the a bit in addition to whatever bits he already had.

It's user-visible. Before we go anywhere with it, ignoring code issues, 
what UI should this have, assuming we do want this feature (I certianly 
see the utility)

https://rt.central.org/rt/Ticket/Display.html?id=123962