Fix warnings_checker.dart handling of multitests

tests/language/mixin_supertype_subclass2_test.dart

 // Copyright (c) 2016, 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.
 // SharedOptions=--supermixin
 
 // Validate the following test from section 12 ("Mixins") of the spec:
 //
 //     "Let M_A be a mixin derived from a class M with direct superclass
 //     S_static.
 //
 //     Let A be an application of M_A.  It is a static warning if the
 //     superclass of A is not a subtype of S_static."
 
 class B {}
 class C {}
 class D {}
 class E extends B with C implements D {}
 class F extends E {}
 class A extends E with M {}
 class M
-  extends B /// 01: ok
-  extends C /// 02: static type warning
-  extends D /// 03: ok
-  extends E /// 04: ok
-  extends F /// 05: static type warning
+  extends B //# 01: ok
+  extends C //# 02: static type warning
+  extends D //# 03: ok
+  extends E //# 04: ok
+  extends F //# 05: static type warning
   {}
 
 main() {
   new A();
 }