Fix warnings_checker.dart handling of multitests

tests/language_strong/literal_unary_plus_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.
 
 // There is no unary plus operator in Dart.
 // Only a number literal can be preceded by a "+'".
 
 main() {
-  var a = + 1; //      /// 01: compile-time error
-  var x = +"foo"; //   /// 02: compile-time error
-  var x = + "foo"; //  /// 03: compile-time error
+  var a = + 1; //      //# 01: compile-time error
+  var x = +"foo"; //   //# 02: compile-time error
+  var x = + "foo"; //  //# 03: compile-time error
 }