does not work with js aggregation enabled and allow_url_fopen=off

When javascript aggregation is on and allow_url_fopen=off widget can't retrieve the JavaScript.

Warning: file_get_contents(http://www.jzuyderduyn.nl/sites/default/files/twitter_block/widgets.js) [function.file-get-contents]: failed to open stream: Connection refused in _locale_parse_js_file() (regel 1488 van /home/vhosts/jzuyderduyn.nl/httpdocs/includes/locale.inc).

Instead we should simply use drupal_add_js('http://platform.twitter.com/widgets.js', 'external');