Ensure that instances of 'AllPermissionsList' are iterable.

[tseaver]

Closes #3073.

[mmerickel]

The permissions in the ACLAuthorizationPolicy are allowed to be iterables of permissions. This object is clearly just trying to support that contract such that the object looks like an iterable even if it doesn't define any permissions itself.

The __contains__ is by far the most important method in the policy and is used in

pyramid/pyramid/authorization.py

Line 131 in cc8ce57

if (ace_action == Allow) and (permission in ace_permissions):

.

Arguably the object itself could just override __eq__ and the policy would wrap it in a list and iterate with ==. I'd argue that the __contains__ + __iter__ is a micro-optimization here. Would you agree @tseaver or do you think the object being iterable is more important? The exposed API is actually ALL_PERMISSIONS which doesn't need to be a "list" at all I think. The class could just as easily be called AllPermissions.

I think this PR is the correct fix if we agree that dropping __contains__ and __iter__ entirely is too much of an incompatibility.

[mmerickel]

It seems no one wants to talk about that. Ah well.