MDL-43952 Javascript: Support invalidation of browser caches for YUI patching

This will also force files loaded from the CDN to instead come from the
local distribution since those patches will not be included in the CDN
release.

Please see the documentation at http://docs.moodle.org/dev/YUI/Patching for
important on using these changes.

lib/setup.php

@@ -349,6 +349,15 @@ if (!defined('AJAX_SCRIPT')) {
 $CFG->yui2version = '2.9.0';
 $CFG->yui3version = '3.13.0';
 
+// Patching the upstream YUI release.
+// For important information on patching YUI modules, please see http://docs.moodle.org/dev/YUI/Patching.
+// If we need to patch a YUI modules between official YUI releases, the yuipatchlevel will need to be manually
+// incremented here. The module will also need to be listed in the yuipatchedmodules.
+// When upgrading to a subsequent version of YUI, these should be reset back to 0 and an empty array.
+$CFG->yuipatchlevel = 0;
+$CFG->yuipatchedmodules = array(
+);
+
 // Store settings from config.php in array in $CFG - we can use it later to detect problems and overrides.
 if (!isset($CFG->config_php_settings)) {
     $CFG->config_php_settings = (array)$CFG;