No way to inherit permissions of built-in types in subtypes.

[Gavin Panella]

Subclasses of frozenset don't appear to be magically granted those
permissions given to frozenset, and there doesn't seem to be a
ready-made interface for frozenset that I could inherit from. (There
is IFrozenSet in zope.schema but it's an IField subclass.)

The frozenset checker can be obtained by calling:

  from zope.security import checker
  checker = checker.getCheckerForInstancesOf(frozenset)

It defines permissions for the following names:

  __and__ __contains__ __eq__ __ge__ __gt__ __iter__ __le__ __len__
  __lt__ __ne__ __or__ __rand__ __ror__ __rsub__ __rxor__ __str__
  __sub__ __xor__ copy difference intersection issubset issuperset
  symmetric_difference union

I could define an interface for this and use it when declaring
permissions on my subtype, or when defining the interface for my
subtype. This seems... wrong, but would work okay. I suppose I could
write a test to ensure that the interface definition keeps up-to-date
with the names defined in Zope's default frozenset checker.

Anyway, without this interface, writing ZCML becomes tedious. For now
I've opted for registering custom checkers (see lp_sitecustomize for
some other jiggery pokery in the same vein) while I seek a better
solution.

Here's my hack:

  from zope.security import checker
  checker_for_frozen_set = checker.getCheckerForInstancesOf(frozenset)
  checker_for_subscriber_set = checker.NamesChecker(["sorted"])
  checker_for_subscription_set = checker.NamesChecker(
      ["sorted", "subscribers"])
  checker.BasicTypes[BugSubscriberSet] = checker.MultiChecker(
      (checker_for_frozen_set.get_permissions,
       checker_for_subscriber_set.get_permissions))
  checker.BasicTypes[BugSubscriptionSet] = checker.MultiChecker(
      (checker_for_frozen_set.get_permissions,
       checker_for_subscription_set.get_permissions))
  checker.BasicTypes[StructuralSubscriptionSet] = checker.MultiChecker(
      (checker_for_frozen_set.get_permissions,
       checker_for_subscription_set.get_permissions))