Add mock-ajax.js to Jasmine 2.0.0.

This PR adds Pivotal's Ajax plugin to the Jasmine test suite library.  Homepage: https://github.com/pivotal/jasmine-ajax

The file was downloaded from [the most recent GitHub commit](https://github.com/pivotal/jasmine-ajax/blob/7bf2ab6a9971207ce8578a7b0ebc977debcca6d6/lib/mock-ajax.js), and the version number (2.0.0) was retrieved from [the most recent `package.json`](https://github.com/pivotal/jasmine-ajax/blob/7bf2ab6a9971207ce8578a7b0ebc977debcca6d6/package.json).

I didn't create a separate library for this beacuse it's made by the same people as Jasmine, and because it's [actually included](http://jasmine.github.io/2.0/ajax.html) in the official Jasmine docs.

I did not minify `mock-ajax.js` because [none](http://cdnjs.cloudflare.com/ajax/libs/jasmine/2.0.0/boot.js) [of](http://cdnjs.cloudflare.com/ajax/libs/jasmine/2.0.0/console.js) [the](//cdnjs.cloudflare.com/ajax/libs/jasmine/2.0.0/jasmine-html.js) [other](//cdnjs.cloudflare.com/ajax/libs/jasmine/2.0.0/jasmine.js) [Jasmine files](http://cdnjs.com/libraries/jasmine/) have minified versions.