Lock/unlock of db breaks if pytest is executed twice in the same process (fixes #1147)

[boxed]

No description provided.

[bluetech]

Thanks for the patch, I can see the problem this is fixing.

I would prefer another fix. The problem occurs because, in order to block DB access by default, pytest-django runs an initial block() in _setup_django(), but doesn't restore it at the end, so it sticks around. The correct fix IMO is to add a restore to balance the _setup_django one, probably in a pytest_unconfigure hook. DjangoDbBlocker by itself is good.

Would you mind trying it?

[boxed]

Hmm. Yea that seems better. Although there is something iffy with the code as it is now, because the setting of the original ensure connection function isn't guaranteed to set the original function every time. Maybe an assert that the __module__ of the function is what we expect might be nice too?

[boxed]

This change works on my test project and I think this is what you meant in your comment above.

[bluetech]

Thanks!