New headers and parameters from RFC 3455 and UUI drafts

These changes derive from mail by John Gregg (see http://list.resiprocate.org/archive/resiprocate-devel/msg08665.html). I added additional header to exchange User-to-User information via SIP.
I wonder if we should just avoid keeping generated code in the repository?  Then it will be easier to review diffs like this one.