Fix warnings_checker.dart handling of multitests

tests/language/mixin_illegal_cycles_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.
 
 class M { }
-class M0 extends Object with M0 { } // /// 01: compile-time error
-class M1 = Object with M1; //        /// 02: compile-time error
+class M0 extends Object with M0 { } // //# 01: compile-time error
+class M1 = Object with M1; //        //# 02: compile-time error
 
-class M2 = Object with M3; //        /// 03: compile-time error
-class M3 = Object with M2; //        /// 03: continued
+class M2 = Object with M3; //        //# 03: compile-time error
+class M3 = Object with M2; //        //# 03: continued
 
-class M4 = Object with M5; //        /// 04: compile-time error
-class M5 = Object with M6; //        /// 04: continued
-class M6 = Object with M4; //        /// 04: continued
+class M4 = Object with M5; //        //# 04: compile-time error
+class M5 = Object with M6; //        //# 04: continued
+class M6 = Object with M4; //        //# 04: continued
 
-class M7 extends Object with M8 { } // /// 05: compile-time error
-class M8 extends Object with M7 { } // /// 05: continued
+class M7 extends Object with M8 { } // //# 05: compile-time error
+class M8 extends Object with M7 { } // //# 05: continued
 
-class M9  = Object with M91; //      /// 06: compile-time error
-class M91 = Object with M92; //      /// 06: continued
-class M92 = Object with M91; //      /// 06: continued
+class M9  = Object with M91; //      //# 06: compile-time error
+class M91 = Object with M92; //      //# 06: continued
+class M92 = Object with M91; //      //# 06: continued
 
 main() {
-  new M0(); // /// 01: continued
+  new M0(); // //# 01: continued
 
-  new M1(); // /// 02: continued
+  new M1(); // //# 02: continued
 
-  new M2(); // /// 03: continued
-  new M3(); // /// 03: continued
+  new M2(); // //# 03: continued
+  new M3(); // //# 03: continued
 
-  new M4(); // /// 04: continued
-  new M5(); // /// 04: continued
-  new M6(); // /// 04: continued
+  new M4(); // //# 04: continued
+  new M5(); // //# 04: continued
+  new M6(); // //# 04: continued
 
-  new M7(); // /// 05: continued
-  new M8(); // /// 05: continued
+  new M7(); // //# 05: continued
+  new M8(); // //# 05: continued
 
-  new M9(); // /// 06: continued
+  new M9(); // //# 06: continued
 }