alternative-status-menu: unpack the result of CanHibernate

The DBus call yields a GVariant, which we need to unpack to
obtain the JS value to compare.

https://bugzilla.gnome.org/show_bug.cgi?id=702300

extensions/alternative-status-menu/extension.js

@@ -47,7 +47,7 @@ function loginManager_canHibernate(asyncCallback) {
                              let result, error;
 
                              try {
-                                 result = proxy.call_finish(asyncResult);
+                                 result = proxy.call_finish(asyncResult).deep_unpack();
                              } catch(e) {
                                  error = e;
                              }