jQuery 1.9+ compatibility fix

From the [jQuery docs](http://api.jquery.com/jquery.browser/):

> jQuery.browser was removed in jQuery 1.9 and is available only through the jQuery.migrate plugin. Please try to use feature detection instead.

This pull request fixes a bug for users of jQuery 1.9+ by first checking if the `browser` function exists for jQuery. To support graceful degradation for IE6 with a later version of jQuery, you will need to use the jQuery.migrate plugin.