Fix warnings_checker.dart handling of multitests

tests/language/private_super_constructor_test.dart

Index: tests/language/private_super_constructor_test.dart
diff --git a/tests/language/private_super_constructor_test.dart b/tests/language/private_super_constructor_test.dart
index a203f4aba665eb7b7ab2ca306dea40062a44c3d7..24b0b1d318d893f9a739851b09a15dc6d9211c69 100644
--- a/tests/language/private_super_constructor_test.dart
+++ b/tests/language/private_super_constructor_test.dart
@@ -7,7 +7,7 @@ library private_super_constructor_test;
 import 'private_super_constructor_lib.dart';
 
 class C extends B {
-  C() : super._foo(); /// 01: compile-time error
+  C() : super._foo(); //# 01: compile-time error
 }
 
 main() => new C();