Handle custom form fields

[aklos]

Hi,
Currently an object form is fetched using self.get_form(request, obj) but this results in field errors when you have custom fields which aren't defined in the model. I've been getting around this issue by replacing get_form() with admin_site._registry[model].form but I'm not sure if it's safe.

[bufke]

I can't commit time here, but if you can I'd accept a pull request. Honestly this is a very old project that I copied from a blog and modernized a little bit. The entire code base could probably be done better and allow for more edge cases.