Since applications that aren't installed no longer have an application
configuration, it is now always True in practice.
Provided an abstraction to temporarily add or remove applications as
several tests messed with app_config.installed to achieve this effect.
For now this API is _-prefixed because it looks dangerous.
* Removed ADMIN_FOR setting and warn warning
* Group view functions by namespace instead of site
* Added a test verifying namespaces are listed
Thanks to Claude Paroz for reviewing and ideas for improvement.
Added comments in the three empty models.py files that are still needed.
Adjusted the test runner to add applications corresponding to test
labels to INSTALLED_APPS even when they don't have a models module.
Don't set a global default interpreted role function for reStructuredText.
Instead, use the `default-role` directive to change the default only within
the `parse_rst()` function.
Thanks Malcolm Tredinnick for the report.
