* Converted the ``libraries`` and ``builtins`` globals of
``django.template.base`` into properties of the Engine class.
* Added a public API for explicit registration of libraries and builtins.
A deprecation path is required because the return type of
django.template.loader.get_template changed during the
multiple template engines refactor.
test_csrf_token_in_404 was incorrect: it tested the case when the
hardcoded template was rendered, and that template doesn't depend on the
CSRF token. This commit makes it test the case when a custom template is
rendered.
This is the expected behavior, but given RequestContext's tortuous
implementation, a straightforward use of its API results in the
opposite.
This commits fixes a regression that must have happened at different
points in the multiple templates engine refactor for different features.
