Fix warnings_checker.dart handling of multitests

tests/language_strong/const_switch_test.dart

   // Copyright (c) 2014, 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.
 
 import 'package:expect/expect.dart';
 
 class C {
   final field;
   const C(this.field);
 }
 
 const c1 = const C(0.0);
 const c2 = const C(0);
 const c3 = const C(0.5 + 0.5);
 const c4 = const C(1);
 
 main() {
-  Expect.equals('0.0', test(c1)); /// 01: ok
-  Expect.equals('0', test(c2)); //  /// 02: ok
-  Expect.equals('1.0', test(c3)); /// 03: ok
-  Expect.equals('1', test(c4)); //  /// 04: ok
+  Expect.equals('0.0', test(c1)); //# 01: ok
+  Expect.equals('0', test(c2)); //  //# 02: ok
+  Expect.equals('1.0', test(c3)); //# 03: ok
+  Expect.equals('1', test(c4)); //  //# 04: ok
 }
 
 String test(C c) {
   switch (c) {
     case const C(0.0): return '0.0';
     case const C(0): return '0';
     case const C(1.0): return '1.0';
     case const C(1): return '1';
   }
   return null;
 }