Fix warnings_checker.dart handling of multitests

tests/language_strong/stacktrace_rethrow_error_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.
 
 class SubclassOfError extends Error {}
 
 fail() => throw "Fail";
 
 // == Rethrow, skipping through typed handlers. ==
 
 aa1() {
   try {
     bb1();
     fail();
   } catch(error
-          , stacktrace // /// withtraceparameter: ok
+          , stacktrace // //# withtraceparameter: ok
           ) {
     expectTrace(['gg1', 'ff1', 'ee1', 'dd1', 'cc1', 'bb1', 'aa1'], error.stackTrace);
-    expectTrace(['gg1', 'ff1', 'ee1', 'dd1', 'cc1', 'bb1', 'aa1'], stacktrace); // /// withtraceparameter: continued
+    expectTrace(['gg1', 'ff1', 'ee1', 'dd1', 'cc1', 'bb1', 'aa1'], stacktrace); // //# withtraceparameter: continued
   }
 }
 
 bb1() => cc1();
 
 cc1() {
   try {
     dd1();
   } on String catch(e) {
     fail();
@@ skipping 16 matching lines @@
 
 gg1() => throw new SubclassOfError();
 
 // == Rethrow, rethrow again in typed handler. ==
 
 aa2() {
   try {
     bb2();
     fail();
   } catch(error
-          , stacktrace // /// withtraceparameter: continued
+          , stacktrace // //# withtraceparameter: continued
           ) {
     expectTrace(['gg2', 'ff2', 'ee2', 'dd2', 'cc2', 'bb2', 'aa2'], error.stackTrace);
-    expectTrace(['gg2', 'ff2', 'ee2', 'dd2', 'cc2', 'bb2', 'aa2'], stacktrace); // /// withtraceparameter: continued
+    expectTrace(['gg2', 'ff2', 'ee2', 'dd2', 'cc2', 'bb2', 'aa2'], stacktrace); // //# withtraceparameter: continued
   }
 }
 
 bb2() => cc2();
 
 cc2() {
   try {
     dd2();
   } on SubclassOfError catch(e) {
     rethrow;
@@ skipping 16 matching lines @@
 
 gg2() => throw new SubclassOfError();
 
 // == Rethrow, with intervening catch without a trace parameter.
 
 aa3() {
   try {
     bb3();
     fail();
   } catch(error
-          , stacktrace // /// withtraceparameter: continued
+          , stacktrace // //# withtraceparameter: continued
          ) {
     expectTrace(['gg3', 'ff3', 'ee3', 'dd3', 'cc3', 'bb3', 'aa3'], error.stackTrace);
-    expectTrace(['cc3', 'bb3', 'aa3'], stacktrace); // /// withtraceparameter: continued
+    expectTrace(['cc3', 'bb3', 'aa3'], stacktrace); // //# withtraceparameter: continued
   }
 }
 
 bb3() => cc3();
 
 cc3() {
   try {
     dd3();
   } catch(e) {
     throw e;
@@ skipping 36 matching lines @@
       expectedIndex++;
     }
   }
 }
 
 main() {
   aa1();
   aa2();
   aa3();
 }