django_orm.py: python 3 compatibility

[amezin]

Fixes #168 for me. Also, fix FlowField the same way.

[nathanielmanistaatgoogle]

You say "Fixes #168 for me" - how about test coverage so that this change can be said to fix #168 for everyone? :-)

[amezin]

I've added two tests (one for each field class) that check field's metaclass.

But they won't improve coverage. Because problematic lines (__metaclass__ =) were already "covered".

Actually, I think, there should be tests that perform write to temporary (in-memory) database, and then try to read the data back. But I have no idea how to setup necessary Django environment in the test.

[dhermes]

How would you set up the necessary environment if it wasn't in a test? Maybe we can help you get it working with tox / unittest / nose. FWIW there are probably existing plugins / test harnesses.

[amezin]

If it wasn't in a test, I'd create a Django project, and run everything (including tests) using django-admin or ./manage.py. All I know is that django does a lot of setup before calling my code. I've found one tool that probably can run django tests as a part of nose test suite: https://pypi.python.org/pypi/NoseDjango. But it haven't been updated for a long time, works only with python 2 and years old versions of django.