Adds generators support for email backends that do not support it.
Fix Python 3 support
Added missing deprecation note for model permission methods.

refs #20642.
Removed warnings level handling code as per deprecation TL.
Removed AuthenticationForm.check_for_test_cookie() as per deprecation TL.
Removed daily_cleanup.py script as per deprecation TL.
Removed django.utils.simplejson as per deprecation TL.
Removed django.utils.itercompat.product() as per deprecation TL.
Removed 'cleanup' management command as per deprecation TL.
Stop auto-correcting string INSTALLED_APPS, TEMPLATE_DIRS settings, as per deprecation TL.
Removed custom profile model functionality as per deprecation TL.
Removed 'depth' .select_related() argument as per deprecation TL.
Removed 'mimetype' arguments from a few places, as per deprecation TL.

This includes HttpResponse and co. __init__() methods,
django.shortcuts.render_to_response() and the index(), sitemap() sitemap
app views.
Removed insert(), value_for_insert() SortedDict methods deprecated in Django 1.5.
Made GeoDjango GeometryField stop accepting a 'null' keyword argument as per its deprecation in 1.5.
Removed django.utils.encoding.StrAndUnicode class, deprecated in Django 1.5.
Fixed 1.6 release notes.
Removed obsolete comment. Refs #20079.

Thanks Gavin Wahl.
More import removals

Following the series of commits removing deprecated features in
Django 1.7, here are some more unneeded imports removed and other
minor cleanups.
Removed comment from setup.cfg which broke newer wheel versions.