Escape story fields and clean story HTML with HTML Purifier.

Add HTML Purifier 4.19.1. Stories are purified when they are saved and
when they are shown.

lib/htmlpurifier-4.19.1/library/HTMLPurifier.autoload.php

@@ -0,0 +1,25 @@
+<?php
+
+/**
+ * @file
+ * Convenience file that registers autoload handler for HTML Purifier.
+ * It also does some sanity checks.
+ */
+
+if (function_exists('spl_autoload_register') && function_exists('spl_autoload_unregister')) {
+    // We need unregister for our pre-registering functionality
+    HTMLPurifier_Bootstrap::registerAutoload();
+    if (function_exists('__autoload')) {
+        // Be polite and ensure that userland autoload gets retained
+        spl_autoload_register('__autoload');
+    }
+} elseif (!function_exists('__autoload')) {
+    require dirname(__FILE__) . '/HTMLPurifier.autoload-legacy.php';
+}
+
+// phpcs:ignore PHPCompatibility.IniDirectives.RemovedIniDirectives.zend_ze1_compatibility_modeRemoved
+if (ini_get('zend.ze1_compatibility_mode')) {
+    trigger_error("HTML Purifier is not compatible with zend.ze1_compatibility_mode; please turn it off", E_USER_ERROR);
+}
+
+// vim: et sw=4 sts=4