Make sure we add the Event header for CoreShowChannels.

(closes issue #13334)
Reported by: srt
Patches:
      13334_missing_event_header_in_core_show_channel.diff uploaded by srt (license 378)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@158414 65c4cc65-6c06-0410-ace0-fbb531ad65f3