Fixed #15012 -- Added post-rendering callbacks to TemplateResponse so that decorators (in particular, the cache decorator) can defer processing until after rendering has occurred. Thanks to Joshua Ginsberg for the draft patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15295 bcc190cf-cafb-0310-a4f2-bffc1f526a37