Issue 2: proposal v11

Attached.

I accepted changes from v10 and made additional changes as I was tasked 
to do during the last call. This should address all the comments/issues 
so far except for one, which is the name of the WS-Policy assertion.

I have changed it from sca:CallbackAssertion to sca:WSCallback. My 
rationale for this is:
1) 'Assertion' is redundunt, so removal just makes it shorter and 
shorter is better.
2) This is a callback mechanism that is defined for Web services. Other 
bidnings/technologies that are used in SCA may have a different 
mechanism for callback so the previx 'WS' makes sense. This constrains 
it to the realm of Web services.

The other suggestion that was made by Mike was 
sca:CallbackAssertion_WSA. I prefer a WS (or WSA) prefix rather than a 
suffix and the underscore is unnecessary. So I suppose another 
alternative would be 'sca:WSACallback'.

-Anish
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