Perform proper handling of forked outbound INVITE requests.

RFC3261 section 12 about dialog creation says an INVITE transaction
results in an established dialog once it receives the 200 OK response.
It is possible to receive multiple differing 200 OK responses for a
single outbound INVITE Request, and this should result in establishing
multiple dialogs.

This patch allows for all differing 200 OK responses to an INVITE request
to establish a separate dialog, but only the first dialog is kept. All other
resulting dialogs from the initial request are immediately ACKed and then
immediately terminated with a BYE request.

Review: https://reviewboard.asterisk.org/r/946/



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@294083 65c4cc65-6c06-0410-ace0-fbb531ad65f3