Add the Uniqueid header to Userevent.

(closes issue #16962)
Reported by: jlpedrosa
Patches:
      patch.diff uploaded by jlpedrosa (license 1002)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@317915 65c4cc65-6c06-0410-ace0-fbb531ad65f3