Fix warnings_checker.dart handling of multitests

tests/language_strong/super_operator_index_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.
 
 // Test that we emit warnings for unresolved indexing operations on super.
 
 class A {
   operator[]=(a, b) {}
 }
 
 class B extends A {
   foo() {
     super[4] = 42;
-    super[4] += 5; /// 01: static type warning, runtime error
-    return super[2]; /// 02: static type warning, runtime error
+    super[4] += 5; //# 01: static type warning, runtime error
+    return super[2]; //# 02: static type warning, runtime error
   }
 }
 
 class C {
   operator[](a) {}
 }
 
 class D extends C {
   foo() {
-    super[4] = 42; /// 03: static type warning, runtime error
-    super[4] += 5; /// 04: static type warning, runtime error
+    super[4] = 42; //# 03: static type warning, runtime error
+    super[4] += 5; //# 04: static type warning, runtime error
     return super[2];
   }
 }
 
 class E {
   foo() {
-    super[4] = 42; /// 05: static type warning, runtime error
-    super[4] += 5; /// 06: static type warning, runtime error
-    return super[2]; /// 07: static type warning, runtime error
+    super[4] = 42; //# 05: static type warning, runtime error
+    super[4] += 5; //# 06: static type warning, runtime error
+    return super[2]; //# 07: static type warning, runtime error
   }
 }
 
 main() {
   new B().foo();
   new D().foo();
   new E().foo();
 }