Use Intl.js Polyfill as `Intl` mock in unit tests

[ericf]

Formatted output differs across implementations; e.g. IE11 adds bidi chars: http://stackoverflow.com/questions/25574963/ies-tolocalestring-has-strange-characters-in-results

Therefore makes it difficult to unit test just these helpers. In order to overcome these problems, we can simply force the use of the Intl.js Polyfill as an Intl mock.

[yahoocla]

CLA is valid!

[drewfish]

+1

[caridy]

+1