bug 3978 --- updated proposal from maryann and dave o.

All,
I worked with Dave O. on a revised proposal for this bug for which I 
attach the following diff of section 3.8.

Justification: The current text  does not completely explain the 
difference
between extending the policy framework itself, and using extensibility 
points
to allow policy expression authors to version policy assertions.

Target: Primer 

Proposal: Change text in section 3.8 as follows: