[1.3.X] Fixes regression #15721 -- {% include %} and RequestContext not...

[1.3.X] Fixes regression #15721 -- {% include %} and RequestContext not working together. Refs #15814.

Backport of r16031, plus the utility from r16030.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.3.X@16089 bcc190cf-cafb-0310-a4f2-bffc1f526a37