Remove the detail=None from APIException signature

The documentation not match with the implementation. The APIException doesn't have detail parameter in the constructor class, actually doesn't have constructor method at all.
Merge pull request #1189 from jespino/patch-1

Remove the detail=None from APIException signature
Add invite signup
Merge branch 'master' of https://github.com/tomchristie/django-rest-framework
Added .  Closes #1188.
Use lookup_url_kwarg in presave if required