RE: [XACML-Usecase] Use case consolidation

Here is a slightly improved version - use this doc. as a catchall
that will give us the broad picture of the use cases with
pointers to each use case to get to the detail.
There is no attempt to analyze these use cases in this round -
though I can see some common reqs. That will of course be the next step.

Cheers,
-Suresh