Fix warnings_checker.dart handling of multitests

tests/language_strong/mixin_cyclic_test.dart

 // Copyright (c) 2013, 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.
 
 // Test for cyclicity check on named mixin applications.
 
 class A<T> {}
 
 class S {}
 class M<T> {}
 
 class C1 = S with M;
-class C2 = S with C2; /// 01: compile-time error
+class C2 = S with C2; //# 01: compile-time error
 class C3 = S with M implements A;
-class C4 = S with M implements C4; /// 02: compile-time error
+class C4 = S with M implements C4; //# 02: compile-time error
 
 void main() {
   new C1();
-  new C2(); /// 01: continued
+  new C2(); //# 01: continued
   new C3();
-  new C4(); /// 02: continued
+  new C4(); //# 02: continued
 }