Django SearchModelAdminMixin doesn't implement each_context

There is a method on Django's (1.8.2) AdminSite class called each_context which provides a context for each and every view in the Django admin. This features comes in handy when you're overriding admin templates and you want to make data (or whatever) globally available to your templates.

The changelist view-overriding that takes place in Haystack's SearchModelAdminMixin unfortunately doesn't call each_context, so any customization you do to each_context is lost when a search is submitted.

The recreate the issue:

1. Implement a custom AdminSite object ( https://docs.djangoproject.com/en/1.8/ref/contrib/admin/#adminsite-objects ), and implement a custom each_context method ( https://docs.djangoproject.com/en/1.8/ref/contrib/admin/#django.contrib.admin.AdminSite.each_context ) and spit out an extra context variable.
2. Override a globally used admin template (say, anything in base.html) and include the extra context variable you added to each_context.
3. Configure an admin using Haystack's SearchModelAdmin.
   4 Try to submit a search to your model's list view and note that your custom context variable is lost.

Start by locating SearchModelAdminMixin and its changelist override, then compare its context handling with Django 1.8 AdminSite.each_context. Reproduce the issue with a custom AdminSite and overridden admin template; done means the custom context variable remains available after submitting a search.