- Adding some refer state definitions from the siptransfer branch

- A bit more URI conversions 
- Changes to sip_dual and the SIP invite structure
- Add Supported: headers to more requests


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@19578 65c4cc65-6c06-0410-ace0-fbb531ad65f3