Merging implementation of invite states from my "invitestate" branch for 1.2. This...

Merging implementation of invite states from my "invitestate" branch for 1.2. This is a bit more
clean platform for the handling of BYE/CANCEL than what we had. It might also need to changes
in other parts of the code, since we know the state of the INVITE transaction.

Please observe that this is is not dialog states at all, this is INVITE transaction states.

Hello Michael Proctor, and thank you! :-)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@47740 65c4cc65-6c06-0410-ace0-fbb531ad65f3