Revert "remove htmlpurifier"

This reverts commit c21a462d52.

lib/htmlpurifier/library/HTMLPurifier/DefinitionCache/Null.php

@@ -0,0 +1,39 @@
+<?php
+
+/**
+ * Null cache object to use when no caching is on.
+ */
+class HTMLPurifier_DefinitionCache_Null extends HTMLPurifier_DefinitionCache
+{
+
+    public function add($def, $config) {
+        return false;
+    }
+
+    public function set($def, $config) {
+        return false;
+    }
+
+    public function replace($def, $config) {
+        return false;
+    }
+
+    public function remove($config) {
+        return false;
+    }
+
+    public function get($config) {
+        return false;
+    }
+
+    public function flush($config) {
+        return false;
+    }
+
+    public function cleanup($config) {
+        return false;
+    }
+
+}
+
+// vim: et sw=4 sts=4