If importing or initializing a template backend fails, attempting to
access this template backend again must raise the same exception.
Backport of 44ad6915 from master
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.
