Add support for generating a ringing sound on an incoming call. This is a bit

Add support for generating a ringing sound on an incoming call.  This is a bit
of a hack.  It just asks the core to generate the same tone that it would when
you hear ringback when making an outbound call.  But hey, it works, and you get
the localized ring tone for the appropriate language set on the channel.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@96079 65c4cc65-6c06-0410-ace0-fbb531ad65f3