Supported JSONP

platform:  # supported: 2.0.4, 2.1.6, 2.2.3
backlogs:  # supported: 0.9.36
ruby:  # supported: 1.9.3, 1.8.7

Fixed a crush when getting issues with JSONP request.
[JSONP-Support](http://www.redmine.org/projects/redmine/wiki/Rest_api#JSONP-Support)