A MediaWiki directory lister extension

I wrote this simple Mediawiki extension that lists the directories contained in a hardwired directory: its output is like the following XHTML list:

<ul>
<li>http://www.foo.org/aaa/</li>
<li>http://www.foo.org/aab/</li>
<li>...</li>
<li>http://www.foo.org/zzz/</li>
</ul>

The directories are returned in the order in which they are stored by the filesystem. Change the values of $dir and $url_foo before using the extension.