[patch] admin does not allow omitting fields in Admin.fields list

[marcink@…]

I ran into this trying to do something in similar vein to Luke Holt's fields-varying-with-user
hack.

The admin app assumes that all of the model's fields are present on the edit page, so
if you don't put a field somewhere in Model.Admin.fields then Django will try to set it
to null every time you try to modify an instance through the admin interface. I fixed this
by changing admin's change_stage function to create follow parameter for the ChangeManipulator
using values from Model.Admin.fields lists.

Not fully tested yet, I'm putting the patch here hoping that someone will let me know if this
is a bad idea.

[Simon G. <dev@…>]

Thanks for the patch marcink, but I'm marking this as wontfix - the newforms admin should fix this.