Add the rxgk-afs draft

Verison 01 from tools.ietf.org.

Change-Id: I60a7cc4db62f3b7328f013755598552f7873b8e8
Import rxgk-afs draft from Simon

This is what he sent me, with carriage returns stripped so that
the diff is readable.

Change-Id: Ieba8d3c8d93cfddf58c975f08dcf427fcd359025