Fix warnings_checker.dart handling of multitests

tests/corelib/symbol_test.dart

 // Copyright (c) 2013, 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.
 
 // Basic test of Symbol class.
 
 main() {
   var x;
   print(x = const Symbol('fisk'));
 
   try {
-    print(const Symbol(0)); /// 01: compile-time error
+    print(const Symbol(0)); //# 01: compile-time error
   } on NoSuchMethodError {
     print('Caught NoSuchMethodError');
   } on TypeError {
     print('Caught TypeError');
   }
 
   try {
-    print(const Symbol('0')); /// 02: compile-time error
+    print(const Symbol('0')); //# 02: compile-time error
   } on ArgumentError catch (e) {
     print('Caught $e');
   }
 
   try {
-    print(const Symbol('_')); /// 03: compile-time error
+    print(const Symbol('_')); //# 03: compile-time error
   } on ArgumentError catch (e) {
     print('Caught $e');
   }
 
   try {
     var y = 0;
     print(new Symbol(y));
     throw 'Expected a NoSuchMethodError or a TypeError';
   } on NoSuchMethodError {
     print('Caught NoSuchMethodError');
@@ skipping 44 matching lines @@
   new Symbol('fisk').hashCode as int;
 
   if (new Symbol('fisk').hashCode != x.hashCode) {
     throw "non-const Symbol's hashCode not equal to its const equivalent";
   }
 
   if (new Symbol('') != const Symbol('')) {
     throw 'empty Symbol not equals to itself';
   }
 }