app_bridgeaddchan.c: Make BridgeAdd be more like Bridge

* Made BridgeAdd not hangup the call if there is a problem.
* Reduced message level from warning to verbose for normal exception
cases.
* Added a loop safety check to BridgeAdd.
* Made BridgeAdd set BRIDGERESULT with the status when dialplan is
resumed.

Change-Id: I374d39b8a3edcc794eeb5c6b9f31a01424cdc426