default-content-type not specialized

f83e9d44a4cd1bceb88a1fc7c6a1b28488a953a9 allows default-content-type to return either a &lt;mime-type&gt; or a &lt;string&gt; (and specializes to &lt;string&gt; with "application/octet-stream"), but locator-media-type for &lt;directory-resource&gt; here expects only a &lt;mime-type&gt;.

Add a specialized default-content-type method for &lt;directory-resource&gt; which returns a new &lt;mime-type&gt; of application/octet-stream