Why do we require "jsoncallback=?" and not just the "callback=?" that jQuery defaults to? It would be a lot easier on new developers if their jQuery calls just worked instead of having to append an extra hash.
JSONP doesn't dictate the parameter name. But I suspect when jsonp support was added, the parameter name didn't default to "callback". (Today, this appears to de facto with jquery, dojo, and extjs.)
I'm guessing we would have to make this configureable since it is a potential compat buster.
(In ) fixes #2679 - use de facto standard "callback" for the JSONP callback parameter name
changeset not BC, we should read both jsoncallback and callback parameter for BC