Jingle doesn't detect when other client supports Jingle
Jingle needs to detect when the other user supports Jingle before allowing a Jingle call to be placed. The current behavior is that when you try to call someone without Jingle, it just immediately says "Call Ended".
We should use CAPS to do this. If we can't, we need to use disco.
That IQ error is good to have, obviously. However, we want to detect no Jingle support through caps BEFORE someone tries to place a call. That way we can disable the dial button.