Fix warnings_checker.dart handling of multitests

tests/language/mixin_illegal_object_test.dart

Index: tests/language/mixin_illegal_object_test.dart
diff --git a/tests/language/mixin_illegal_object_test.dart b/tests/language/mixin_illegal_object_test.dart
index fb2c0bd7c1b68f82dc837dc25602099e6bda5bb1..a95bdfa0f42c293b3f5ab7d0050b9ae1f880366b 100644
--- a/tests/language/mixin_illegal_object_test.dart
+++ b/tests/language/mixin_illegal_object_test.dart
@@ -7,12 +7,12 @@
 class S { }
 
 class C0 extends S
-with Object //                      /// 01: compile-time error
+with Object //                      //# 01: compile-time error
 { }
 
-class C1 = S with Object; //        /// 02: compile-time error
+class C1 = S with Object; //        //# 02: compile-time error
 
 main() {
   new C0();
-  new C1(); //                      /// 02: continued
+  new C1(); //                      //# 02: continued
 }