Use Cu.unload where available.

--HG--
extra : rebase_source : 28ce17c49f2eeb6b330ce47e13e0543569348c59

common/modules/util.jsm

@@ -1623,6 +1623,7 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
     rehash: function (args) {
         JSMLoader.commandlineArgs = args;
         this.timeout(function () {
+            services.observer.notifyObservers(null, "startupcache-invalidate", "");
             this.rehashing = true;
             let addon = config.addon;
             addon.userDisabled = true;