Revert "remove htmlpurifier"

This reverts commit c21a462d52.

lib/htmlpurifier/library/HTMLPurifier/AttrDef/URI/Email.php

@@ -0,0 +1,17 @@
+<?php
+
+abstract class HTMLPurifier_AttrDef_URI_Email extends HTMLPurifier_AttrDef
+{
+
+    /**
+     * Unpacks a mailbox into its display-name and address
+     */
+    function unpack($string) {
+        // needs to be implemented
+    }
+
+}
+
+// sub-implementations
+
+// vim: et sw=4 sts=4