Prevent potential infinite recursion in DomainMixin.save().
Prevent potential infinite recursion in DomainMixin.save().

Rewrite DomainMixin.save() in such a way to prevent a potential infinite
recursion. Previously, the save() method invoked save on other DomainMixin
objects. An infinite mutual recursion could occur with two objects, both
with is_primary=True, calling each other's save() methods.

Not sure of the exact conditions that could lead to this behavior.
Nevertheless, better to prevent it.

sigma-geosistemas/django-tenants,tomturner/django-tenants,tomturner/django-tenants,tomturner/django-tenants,sigma-geosistemas/django-tenants