switch to parent-based normalize

Author: guybedford

src/system-register-loader.js

@@ -30,9 +30,10 @@ SystemRegisterLoader.prototype = Object.create(RegisterLoader.prototype);
 // normalize is never given a relative name like "./x", that part is already handled
 // so we just need to do plain name detect to throw as in the WhatWG spec
 SystemRegisterLoader.prototype.normalize = function(key, parent, metadata) {
-  if (key.indexOf(':') === -1)
+  var resolved = RegisterLoader.prototype.normalize.call(this, key, parent, metadata);
+  if (!resolved)
     throw new RangeError('System.register loader does not resolve plain module names, resolving "' + key + '" to ' + parent);
-  return key;
+  return resolved;
 };
 
 var fs;