Revert "remove htmlpurifier"

This reverts commit c21a462d52.

lib/htmlpurifier/library/HTMLPurifier/ConfigSchema/schema/AutoFormat.Linkify.txt

@@ -0,0 +1,12 @@
+AutoFormat.Linkify
+TYPE: bool
+VERSION: 2.0.1
+DEFAULT: false
+--DESCRIPTION--
+
+<p>
+  This directive turns on linkification, auto-linking http, ftp and
+  https URLs. <code>a</code> tags with the <code>href</code> attribute
+  must be allowed.
+</p>
+--# vim: et sw=4 sts=4