ignore js/css/img hosted on a remote server

Hi Ben,

I didn't see a point in hashing href's that are remote URLs, particularly for CDN hosted libraries like AngularJS, jQuery, or Bootstrap.

Here's a copy of my commit msg:

    ignore js/css/img hosted on a remote server

    - cacheBust should ignore files hosted on a CDN as these files typically
      include version strings to identify code changes

    - including a hash value in the querystring at best causes a cache miss
      in the browser, causing the browser to redownload already cached
      version of CDN hosted libraries like jQuery, Bootstrap, or AngularJS;
      at worst, the remote server might alter the response based on a the
      querystring parameter

    - the current cacheBust implementation does not accurately hash remote
      URLs, as it would need to download the URL to a local file first

Thanks,
Steve