MDL-22537 new html purifier backported to stable, unfortunately PHP5 only

lib/setup.php

@@ -92,6 +92,10 @@ global $HTTPSPAGEREQUIRED;
 /// sometimes default PHP settings are borked on shared hosting servers, I wonder why they have to do that??
     @ini_set('precision', 14); // needed for upgrades and gradebook
 
+/// New versions of HTML Purifier are not compatible with PHP 4
+    if (version_compare(phpversion(), "5.0.5") < 0) {
+        $CFG->enablehtmlpurifier = 0;
+    }
 
 /// store settings from config.php in array in $CFG - we can use it later to detect problems and overrides
     $CFG->config_php_settings = (array)$CFG;
@@ -256,7 +260,6 @@ global $HTTPSPAGEREQUIRED;
         $originaldatabasedebug = -1;
     }
 
-
 /// For now, only needed under apache (and probably unstable in other contexts)
     if (function_exists('register_shutdown_function')) {
         register_shutdown_function('moodle_request_shutdown');