Revert "remove htmlpurifier"

This reverts commit c21a462d52.

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

@@ -0,0 +1,18 @@
+<?php
+
+/**
+ * Pre-transform that changes deprecated border attribute to CSS.
+ */
+class HTMLPurifier_AttrTransform_Border extends HTMLPurifier_AttrTransform {
+
+    public function transform($attr, $config, $context) {
+        if (!isset($attr['border'])) return $attr;
+        $border_width = $this->confiscateAttr($attr, 'border');
+        // some validation should happen here
+        $this->prependCSS($attr, "border:{$border_width}px solid;");
+        return $attr;
+    }
+
+}
+
+// vim: et sw=4 sts=4