lookup_url_kwarg not correctly used by Router

[cancan101]

lookup_url_kwarg does not appear to be used by the router when generating URLs. See:
https://github.com/tomchristie/django-rest-framework/blob/ba7dca893cd55a1d5ee928c4b10878c92c44c4f5/rest_framework/routers.py#L228

[lovelydinosaur]

Does look like a defect, yes.
If anyone's able to together a minimal failing test case that's probable the next thing needed to progress this issue.