This work is for solving ticket https://code.djangoproject.com/ticket/19838
Includes tests and patch.
Main idea is to add some validation on the inline-formset.
evidencing the problem on a simple test
modifying get_formset on InlineAdminForm so deletion is validated aga…
…inst Protected items
improved error message making easy i18n it. Cleaned a bit the logic
added myself to authors list
Fixed in 3ea0c7d. Thanks!