resend of corupted Sequence Diagram

I resent the sequence diagram for returnNotAvailable, for the last one 
was corrupted.

This needs to be discussed as an optimization which a sender can use.

It does not need to be visible at the high level state diagram., it can 
be considered part of the mapping to HTTP.

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Tom Rutt		email: ; 
Tel: +1 732 801 5744          Fax: +1 732 774 5133