Expose polyfills as options

By exposing polyfills as a task option, users can provide polyfill libraries such as json2 and querySelector to support old browsers such as IE6 and IE7.
I have pull request https://github.com/pivotal/jasmine/pull/647 with pivotal to fix IE6+7 specific script errors. Once these small changes are merged, then IE6+7 can run Jasmine tests no problem.