Attempt to be more helpful when using a bad ao2 object pointer.

Backport of -r360626 with some enhancements.  Put the external obj pointer
in the message instead of the internal version.


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@379963 f38db490-d61c-443f-a65b-d21fe96a405b