External JavaScript and CSS Manager for Elgg

INTRO
This library provides 2 functions for including external javascript and css files.
It handles including them into the web page and prevents multiple inclusions of
the same file.

USAGE
elgg_register_external_js(<url>, <identifier>);
elgg_register_external_css(<url>, <identifier>);

EXAMPLES
elgg_register_external_js('http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.2/jquery-ui.min.js', 'jquery-ui');
elgg_register_external_js('http://example.org/mod/myplugin/js/jquery.rating.min.js', 'jquery.rating');