Fix Dial m and r options and forked calls generating warnings for voice frames.

Fix Dial m and r options and forked calls generating warnings for voice frames.

When connected line support was added, the wait_for_answer() variable
single changed its meaning slightly.  Unfortunately, the places where
single was used did not necessarily get updated to reflect that change.
Also audio/video frames were sent to all forked calls when the endpoints
were never made compatible.

* Don't pass audio/video media frames when the channels have not been made
compatible.

* Added handling of AST_CONTROL_SRCCHANGE to app_dial.c.

* Fixed app_dial.c passing on AST_CONTROL_HOLD because that frame can also
pass a requested MOH class.

(closes issue ASTERISK-16901)
Reported by: Chris Gentle

(closes issue ASTERISK-17541)
Reported by: clint

Review: https://reviewboard.asterisk.org/r/1805/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@359344 65c4cc65-6c06-0410-ace0-fbb531ad65f3