app_queue crashes randomly, often during call-transfers

app_queue crashes randomly, often during call-transfers

In app_queue, it is possible for a call_queue to be destroyed
while another object still holds a pointer to it.  This patch
converts call_queue objects to ao2 objects allowing them to be
ref counted.  This makes it safe for the queue_ent object in
queue_exec() to reference it's parent call_queue even after it
has left the queue.

(closes issue #15686)
Reported by: Hatrix
Patches:
      v2_queue_ao2.diff uploaded by dvossel (license 671)
Tested by: dvossel, aragon

Review: https://reviewboard.asterisk.org/r/427/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@231437 65c4cc65-6c06-0410-ace0-fbb531ad65f3