Fix Ember global deprecation

A minimal fix for #600. We should probably follow through with the
refactor suggested by @rwjblue in #600 but that can be done later.

assets/browser-fetch.js.t

@@ -1,7 +1,14 @@
 (function (originalGlobal) {
-  define('fetch', ['exports'], function(exports) {
+  if (!require.has('ember')) {
+    define('ember', ['exports'], function(exports) {
+      exports['default'] = originalGlobal.Ember;
+    });
+  }
+
+  define('fetch', ['exports', 'ember'], function(exports, Ember) {
     'use strict';
-    var Promise = originalGlobal.Ember.RSVP.Promise;
+    var Ember__default = 'default' in Ember ? Ember['default'] : Ember;
+    var Promise = Ember__default.RSVP.Promise;
     var supportProps = [
       'FormData',
       'FileReader',
@@ -49,8 +56,8 @@
       return result;
     }
 
-    if (originalGlobal.Ember.Test) {
-      originalGlobal.Ember.Test.registerWaiter(function() {
+    if (Ember__default.Test) {
+      Ember__default.Test.registerWaiter(function() {
         return pending === 0;
       });