Fix warnings_checker.dart handling of multitests

tests/language/toplevel_collision1_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.
 
 int x = 100;
 
-get x => 200; //                /// 00: compile-time error
-set x(var i) { print(i); } //     /// 01: compile-time error
+get x => 200; //                //# 00: compile-time error
+set x(var i) { print(i); } //     //# 01: compile-time error
 
-int x(a, b) { print(a + b); } //  /// 02: compile-time error
+int x(a, b) { print(a + b); } //  //# 02: compile-time error
 
 
 void main() {
   // No need to reference x.
 }