Specify JSONP handling

[philipashlock]

None

[philipashlock]

I think this is pretty much as simple as deciding the name of the parameter. For reference this is the documentation for github on JSON-P Callbacks:

http://developer.github.com/v3/#json-p-callbacks

[peterwtux]

Per a mailing list discussion in August 2012 (http://thread.gmane.org/gmane.comp.standards.open311/555), Connected Bits, CitySourced, and SeeClickFix and others already support the parameter name "callback". Let's just formalize that.