[patch] Add extra_context to admin stages

[plisk]

New admin now allows to override templates, but there is no way to add additional context params to your new templates. Proposed patch adds new param extra_context to change_list, add_stage and change_stage views similar to the one used in generic views.

Also i think loop used to add params to context should be refactored to 1 function, cos its used in many places in generic views and with this patch in 3 places more in admin views. And name it for example django.utils.functional.context_add_extra. Any comments ?

[rjwittams]

This seems kind of odd. How is the extra context going to get filled? It doesn't seem sensible for people to be mashing with the admin url conf.
A better way to get stuff into the context is to make a processor. See #925 which was applied. If your information does not come from the request, you can just make a template tag to fetch it.

[Adrian Holovaty]

Instead of extra_context, use the TEMPLATE_CONTENT_PROCESSORS framework added a couple of days ago:

​http://www.djangoproject.com/documentation/templates_python/#subclassing-context-djangocontext