resip/recon: ConversationManager: support extension headers when creating new remote participant

git-svn-id: https://svn.resiprocate.org/rep/resiprocate/main@11053 ddefafc4-47db-0310-ae44-fa13212b10f2
resip/recon: call acceptNIT() after handling INFO message

git-svn-id: https://svn.resiprocate.org/rep/resiprocate/main@11054 ddefafc4-47db-0310-ae44-fa13212b10f2
resip/recon: call rejectNIT() when we can not process an INFO message

git-svn-id: https://svn.resiprocate.org/rep/resiprocate/main@11055 ddefafc4-47db-0310-ae44-fa13212b10f2
resip/dum: add some comments and a warning about acceptNIT and rejectNIT for SIP INFO

git-svn-id: https://svn.resiprocate.org/rep/resiprocate/main@11056 ddefafc4-47db-0310-ae44-fa13212b10f2