Re: [security-services] Propose addition of a SubjectRef element

I Don't mind adding this.  However, I still prefer that we have an
assertion level subject that applies to all statements implicitly
unless it is overridden by a subject within the statement.

We see that most of the time, the Assertion will have a
single subject (while allowing for those who see otherwise)
and we would like to optimize that case.

Conor