[patch] Allow templates to extend from parents in local context

[clelland@…]

It can be useful for templates to extend a base template which does not necessarily exist on the filesystem -- for example, the base template may be stored in the database, or it may be generated at runtime.

This patch allows a template object in the curent context to be used as a base template for inheritance.

Example:

>>> from django.template import Context, Template, loader
>>> child = Template("{% extends parent %}{% block one %}Hello, {{ name }}{% endblock %}")
>>> parent = Template("<h1>{% block one %}Name{% endblock %}</h1>")
>>> child.render(Context({'name': 'World', 'parent': parent}))

returns "<h1>Hello, World</h1>"

[Jacob]

Fixed in [3465].