Add 'c' option to app_queue which allows for continuing in the dialplan if the callee hangs up.

Issue 9284, patch by lyl, modified a little bit by me (I felt 'continue' was better than 'keepalive')


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@64243 65c4cc65-6c06-0410-ace0-fbb531ad65f3