test rename overhaul: step 7 - corelib tests

tests/corelib/list_sort_test.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #library("ListSortTest.dart");
-#source("SortHelper.dart");
+#source("sort_helper.dart");
 
 class ListSortTest {
   static void testMain() {
     var compare = (a, b) => a.compareTo(b);
     var sort = (list) => list.sort(compare);
     new SortHelper(sort, compare).run();
 
     compare = (a, b) => -a.compareTo(b);
     new SortHelper(sort, compare).run();
   }
 }
 
 main() {
   ListSortTest.testMain();
 }