Fix warnings_checker.dart handling of multitests

tests/language/function_type_alias6_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.
 // Dart test for legally self referencing function type alias.
 
 import "package:expect/expect.dart";
 
 typedef F(List
-              <F> // /// 00: compile-time error
+              <F> // //# 00: compile-time error
                   x);
 
 typedef D C();
 
 class D {
   C foo() { }
   D bar() { }
 }
 
 main() {
   var f = (List x) { };
   Expect.isTrue(f is F);
   var g = (List<F> x) { };
   Expect.isTrue(g is F);
   var d = new D();
   Expect.isTrue(d.foo is !C);
   Expect.isTrue(d.bar is C);
 }