Merge changes from team/russell/sla_trunk_moh ...

* Added the ability to specify the music on hold class used to play into the
   conference when there is only one member and the M option is used.
* Added the ability to specify a music on hold class to play instead of ringing
   for the SLATrunk application.

(patched by me, and tested internally)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@89470 65c4cc65-6c06-0410-ace0-fbb531ad65f3