Fix warnings_checker.dart handling of multitests

tests/language/toplevel_collision2_test.dart

 // Copyright (c) 2011, 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.
 
 
 get x => 200;
 
 // Ok: can have a setter named x when getter x is defined.
 set x(var i) { print(i); }
 
 // Error: there is already a getter for x
-int x; //                         /// 00: compile-time error
+int x; //                         //# 00: compile-time error
 
 // Error: there is already a getter named x.
-int x(a, b) { print(a + b); } //  /// 01: compile-time error
+int x(a, b) { print(a + b); } //  //# 01: compile-time error
 
 
 
 void main() {
   // No need to reference x.
 }