Support option 'n', as applications like Playback, Background etc.

Suggested on asterisk-dev as trivial application change.
 
Reported by: alecdavis
Tested by: alecdavis


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@234976 65c4cc65-6c06-0410-ace0-fbb531ad65f3