Commit of the new SIP transfer support (oej/siptransfer branch)

- improved support of attended transfers (REFER with replaces)
- support of INVITE/replaces in the context of a transfer
- improved support of blind transfers (REFER)

Thanks to Voop, Nuvio and Foniris for sponsoring this work.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@31274 65c4cc65-6c06-0410-ace0-fbb531ad65f3