* Fix missing related managers on some models
I was seeing an issue where some related managers were missing from some
models. Traced the issue down to this line, where it appears that if we
hit a relation with a non-default(?) reverse manager the iteration
stopped. I _think_ this is supposed to be a continue statement instead.
It appears to work in the project I'm working in at least.
* Add test case
* Add test case
* Add datetime to set_type of DateTimeField
`DateTimeField` was missing `datetime` as a valid set type. But Django clearly accepts `datetime`.
* Fix test for DateTimeField type change
datetime is now a valid set type for DateTimeField
