~~drop the patch in DateTime._parse_args which cause DateTime to
support timezone naive dates~~
~~adjust __setstate__ to pickle the timezone naive flag~~

=> no we keep it the same patch as it was, without timezone
native support

adjust code relying on DateTime private attributes

adjust tests for new DateTime.__eq__ behavior (instances with
different timezones are different)

more testing, especially for various __setstate__ versions

introduce a context manager to change timezone in tests.