This allows filter on un-revoked objects. Changes default JSONEncoder to
drop optional properties with default values in the spec if set to the
default value. They can be included by passing
include_optional_defaults=True to serialize().
This is needed to implement functions like `set_default_creator`.
The changes to Tox are so that the wrapping we do in workbench doesn't
affect the rest of our tests. If we test them all in one go, pytest will
import all the tests before running any of them. This will cause the
workbench versions of the SDO classes to be used in all tests.
Chris Lenk