Subject: app_queue

Added a new AMI action: QueueWithdrawCaller
This AMI action makes it possible to withdraw a caller from a queue
back to the dialplan. The call will be signaled to leave the queue
whenever it can, hence, it not guaranteed that the call will leave
the queue.

Optional custom data can be passed in the request, in the WithdrawInfo
parameter. If the call successfully withdrawn the queue,
it can be retrieved using the QUEUE_WITHDRAW_INFO variable.

This can be useful for certain uses, such as dispatching the call
to a specific extension.
