delegation constraints schema

[Simon <sgodik@gluecode.com>]

(See Erik's msg on delegation constraint)
Delegation constraint can be expressed by having <DelegationConstraint> 
element as a child of <Delegate>

Note that constraints on immediate delegate can be applied to 
re-delegates and then delegation-constraint is not needed.

<Target>
    <Delegate>
       <SubjectMatch>....</SubjectMatch> <- ONE OR MORE (Constraints on 
immediate delegate)
       <DelegationConstraint>   <-- OPTIONAL (Constraints on re-delegates)
          <SubjectMatch>....</SubjectMatch>   <-- ONE OR MORE
          <SubjectMatch>...</SubjectMatch>
       </DelegationConstraint>
    </Delegate>
</Target>

Simon