The unit tests for RelationCounterField didn't work properly on newer

versions of Django. The field itself was fine, but the tests needed some

work.
A big part of this was due to a difference in how signals worked on

newer versions of Django. When a weak reference disappeared under Django

1.6, the connections would immediately be cleaned up, but on newer

versions, they'd just be flagged for cleanup the next time connect(),

disconnect(), or _live_receivers() was called, making our

Signal.receivers check fail. The fix for this is to just call

_live_receivers() instead in the tests, which will give us the correct

results and even let us specify the model we care about (simplifying a

lot of test code).
The other problem was that one of the tests no longer made sense in

newer versions of Django. It was testing to make sure that a reused ID

from a Model.delete() call wouldn't cause the wrong state to be looked

up. This could happen due to delete() working within the same

transaction as the caller, but in newer versions of Django, deletions

have their own transaction, preventing this problem.

Unit tests pass on Django 1.6, 1.9, 1.10, and 1.11. For other reasons,

1.7 and 1.8 are not tested.