Actually make URI.DisableResources do something.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

library/HTMLPurifier/ConfigSchema/schema/URI.DisableResources.txt

@@ -1,12 +1,15 @@
 URI.DisableResources
 TYPE: bool
-VERSION: 1.3.0
+VERSION: 4.1.2
 DEFAULT: false
 --DESCRIPTION--
-
 <p>
     Disables embedding resources, essentially meaning no pictures. You can
     still link to them though. See %URI.DisableExternalResources for why
     this might be a good idea.
 </p>
+<p>
+    <em>Note:</em> While this directive has been available since 1.3.0,
+    it didn't actually start doing anything until 4.1.2.
+</p>
 --# vim: et sw=4 sts=4

library/HTMLPurifier/URIFilter/DisableResources.php

@@ -0,0 +1,11 @@
+<?php
+
+class HTMLPurifier_URIFilter_DisableResources extends HTMLPurifier_URIFilter
+{
+    public $name = 'DisableResources';
+    public function filter(&$uri, $config, $context) {
+        return !$context->get('EmbeddedURI', true);
+    }
+}
+
+// vim: et sw=4 sts=4