Enhance AMI redirect to allow channels to be redirected to different places.

New parameters ExtraContext, ExtraExtension, and ExtraPriority have been added
to redirect the second channel to a different location. Previously, it was only
possible to redirect both channels to the same place.

(closes issue #15853)
Reported by: haakon
Patches:
      trunk-manager.c.patch uploaded by haakon (license 880)
Tested by: jpeeler


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@235265 65c4cc65-6c06-0410-ace0-fbb531ad65f3