Fail silently on errors sending e-mail.
Always check media URL.
v0.9.21
Add redis as a requirement; use a Celery transport.
Generate statistics in a background task.

Also updates other tasks to use the shared app
decorator (so that settings are correctly propagated
to unittests).

Also adds a custom test runner to run celery tasks
synchronously.

Issue #214.
Show a warning in case of redis connection problems.