Fix warnings_checker.dart handling of multitests

tests/language_strong/duplicate_implements_test.dart

 // Copyright (c) 2012, 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.
 // Check that duplicate types in implements/extends list are
 // compile-time errors.
 
 abstract class I { }
 abstract class J { }
 abstract class K<T> { }
 
-class X implements I, J, I { } //              /// 01: compile-time error
-class X implements J, I, K<int>, K<int> { } // /// 02: compile-time error
+class X implements I, J, I { } //              //# 01: compile-time error
+class X implements J, I, K<int>, K<int> { } // //# 02: compile-time error
 
-abstract class Z implements I, J, J { } //             /// 03: compile-time error
-abstract class Z implements K<int>, K<int> { } //      /// 04: compile-time error
+abstract class Z implements I, J, J { } //             //# 03: compile-time error
+abstract class Z implements K<int>, K<int> { } //      //# 04: compile-time error
 
 main() {
-  X x = new X(); // /// 01: continued
-  X x = new X(); // /// 02: continued
-  Z z = new Z(); // /// 03: continued
-  Z z = new Z(); // /// 04: continued
+  X x = new X(); // //# 01: continued
+  X x = new X(); // //# 02: continued
+  Z z = new Z(); // //# 03: continued
+  Z z = new Z(); // //# 04: continued
 }