Make System global always.

Otherwise we can't get to it in ES6

Author: johnjbarton

lib/system.js

@@ -217,12 +217,6 @@
   }
   System.paths = { '*': '*.js' };
 
-  if (global.System && global.traceur)
-    global.traceurSystem = global.System;
-
-  if (isBrowser)
-    global.System = System;
-
   // <script type="module"> support
   // allow a data-init function callback once loaded
   if (isBrowser) {
@@ -264,4 +258,8 @@
   if (typeof exports === 'object')
     module.exports = System;
 
+  if (global.System && global.traceur)
+    global.traceurSystem = global.System;
+  global.System = System;
+
 })(typeof global !== 'undefined' ? global : this);