Fix warnings_checker.dart handling of multitests

tests/language/regress_27617_test.dart

 // Copyright (c) 2016, 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 Foo {
   final String greeting;
   Foo._(this.greeting) { }
 
   // Const constructor must not redirect to non-const constructor.
-  const Foo.hi() : this._('hi'); // /// 1: compile-time error
+  const Foo.hi() : this._('hi'); // //# 1: compile-time error
 }
 
 main() {
-  const h = const Foo.hi(); // /// 1: continued
+  const h = const Foo.hi(); // //# 1: continued
 }