[AFS3-std] rxgk draft updates

[Benjamin Kaduk]

In addition to the introduction of RXGK com_err codes, I also pushed a 
couple of commits from Mike Meffie.  The first one is a reordering the 
discussion of auth-only, integrity protection, and encryption for packet 
handling, so as to match up with the order that the security levels are 
introduced in.  There's also some clarification of how packet handling 
works for RXGK_AUTH, along with explicit diagrams for the get_mic input 
blob and the on-the-wire data.  Thanks, Mike!

I also stripped out the carriage returns from the file to apply Mike's 
patches, and so that I don't always have a bunch of blue in my editor as 
I'm working.  This makes reordering patches a bit harder, but I don't 
think it's a problem.

Going back through my emails, I don't have anything else sitting in my 
inbox with concerns about the CombineTokens language.  Simon, is it time 
for a new I-D?

-Ben