Disallowed subobject types (bug)

Sometimes, in portal_types, was necessary uncheck the "Filter content types?", set rule on the folder and select the filter again.

In portal_setup show the same error when I export all steps.

Log error:

Exception Value Disallowed subobject type: Document

Traceback (innermost last):

```
Module ZPublisher.Publish, line 126, in publish
Module ZPublisher.mapply, line 77, in mapply
Module ZPublisher.Publish, line 46, in call_object
Module zope.formlib.form, line 795, in __call__
Module sc.contentrules.groupbydate.actions.groupbydate, line 231, in update
Module zope.formlib.form, line 891, in setUpWidgets
Module zope.formlib.form, line 310, in setUpInputWidgets
Module zope.schema._field, line 291, in bind
Module Zope2.App.schema, line 33, in get
Module sc.contentrules.groupbydate.vocabulary, line 108, in __call__
Module Products.CMFCore.PortalFolder, line 293, in invokeFactory
```

ValueError: Disallowed subobject type: Document