[mail-vet-discuss] Version 08 of draft posted

[Murray S. Kucherawy]

This version incorporates a lot of the recent feedback.  Of particular 
interest:

- a flow diagram in section 1 for clarification of definitions
- minor ABNF corrections
- clarifications around the authentication identifier
- rearrange and rework header addition/removal text
- some changes in the IANA Considerations section
- additional Security Considerations suggesting the ESMTP/IMAP solutions
- add a multi-tiered authentication example