Filter out internal channels for bridge leave messages and parked call messages

Granted, if you manage to park a Conference announcer channel, something has
gone horrifically wrong.
........

Merged revisions 400217 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@400218 65c4cc65-6c06-0410-ace0-fbb531ad65f3