Revised SAP draft submitted

[Colin Perkins <[e-mail]>]

I've just submitted a revision to the session announcement protocol draft,
which addresses the comments I received during working group last call.
Until it appears in the internet-draft archives, the draft is available
from:
http://www.cs.ucl.ac.uk/staff/c.perkins/internet-drafts/draft-ietf-mmusic-sap-v2-05.txt

Summary of changes since the -04 revision:
- Remove references to "client" in the text, now talks about SAP
  announcers and listeners only.
- Clarify that TTL scoping is discouraged (in favour of admin scoping)
- Clarify section on session deletion
- Remove the optional timeout field from the packet format
	- It was only used for encrypted SAP, for those cases where a
	  proxy didn't have the decryption key. 
	- We now rely on either
	 	1) the receiver of an announcement understands the payload,
		and can derive the session timeout from that (this is the
		common case)
	  or	2) the announcer sends explicit deletion packets when it
	   	stops sending the announcement
	  or	3) the receiver will timeout an announcement which hasn't
	  	been heard for some time
	  (proxies which deal with encrypted SAP can still recognize cases
	  2 and 3).
- Clarify why IPsec is not recommended for authentication.
- Update references

Colin