Revert "remove htmlpurifier"

This reverts commit c21a462d52.

lib/htmlpurifier/library/HTMLPurifier/AttrTransform/Nofollow.php

@@ -0,0 +1,45 @@
+<?php
+
+// must be called POST validation
+
+/**
+ * Adds rel="nofollow" to all outbound links.  This transform is
+ * only attached if Attr.Nofollow is TRUE.
+ */
+class HTMLPurifier_AttrTransform_Nofollow extends HTMLPurifier_AttrTransform
+{
+    private $parser;
+
+    public function __construct() {
+        $this->parser = new HTMLPurifier_URIParser();
+    }
+
+    public function transform($attr, $config, $context) {
+
+        if (!isset($attr['href'])) {
+            return $attr;
+        }
+
+        // XXX Kind of inefficient
+        $url = $this->parser->parse($attr['href']);
+        $scheme = $url->getSchemeObj($config, $context);
+
+        if ($scheme->browsable && !$url->isLocal($config, $context)) {
+            if (isset($attr['rel'])) {
+                $rels = explode(' ', $attr);
+                if (!in_array('nofollow', $rels)) {
+                    $rels[] = 'nofollow';
+                }
+                $attr['rel'] = implode(' ', $rels);
+            } else {
+                $attr['rel'] = 'nofollow';
+            }
+        }
+
+        return $attr;
+
+    }
+
+}
+
+// vim: et sw=4 sts=4