Text to insert as section 3.1.3

Attached please find proposed text for section 3.1.3 of
ProposalLast.html (the current 3.1.3 would become 3.1.4).  This text
concerns the behavior of operations in SOAP 1.2 bindings, complementing
the existing 3.1.2, which covers SOAP 1.1/HTTP.  As such, I believe it
can be considered separately from the current discussion.

This is substantially the proposal I sent out earlier, but with a few
editorial changes, most notably:

    * I've retitled the section and redone the introductory paragraph to
      (I hope) fit in with the rest of the document
    * I've re-arranged the rules into two cases (SOAP request-response
      and SOAP one-ways) and added an explanatory sentence, in response
      to Marc's feedback.
    * I've removed the hedging about SOAP one-ways.  The text now
      assumes they exist -- it's considerably less useful otherwise.