features: Don't cache a struct ast_app pointer.

Caching a struct ast_app pointer is not a good idea because someone could
unload the application.  After the applicaiton unload the cached ast_app
pointer is no longer valid.  Only pbx.c can cache the pointer because it
knows when the application is unloaded and removes the pointer.

* Fixed one-touch Monitor and MixMonitor to not cache the ast_app pointer
and not use the silly monitor_ok/mixmonitor_ok/stopmixmonitor_ok flags.

* Extracted bridge_check_monitor() from ast_bridge_call() and use propper
locking.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@381177 65c4cc65-6c06-0410-ace0-fbb531ad65f3