Fix warnings_checker.dart handling of multitests

tests/language/parameter_default_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.
 
 class C {
   foo(a
-      : 1 // /// 01: compile-time error
-      = 1 // /// 02: compile-time error
+      : 1 // //# 01: compile-time error
+      = 1 // //# 02: compile-time error
   ) { print(a); }
 
   static bar(a
-      : 1 // /// 03: compile-time error
-      = 1 // /// 04: compile-time error
+      : 1 // //# 03: compile-time error
+      = 1 // //# 04: compile-time error
   ) { print(a); }
 }
 
 baz(a
-    : 1 // /// 05: compile-time error
-    = 1 // /// 06: compile-time error
+    : 1 // //# 05: compile-time error
+    = 1 // //# 06: compile-time error
 ) { print(a); }
 
 main() {
   foo(a
-      : 1 // /// 07: compile-time error
-      = 1 // /// 08: compile-time error
+      : 1 // //# 07: compile-time error
+      = 1 // //# 08: compile-time error
   ) { print(a); }
 
   foo(1);
 
   new C().foo(2);
 
   C.bar(3);
 
   baz(4);
 }