ratelimit_agent: Fix key expiring too soon.

This caused occasional NOT_FOUNDs on the incr when we were unlucky to
have it expire between the add and the incr.
reddit_base: Fix babel.core import position.

Babel is not a stdlib.
ErrorController: Clean up imports.
ErrorController: Fix Retry-After header not being sent.
Fix race condition in stats flushing.

Some threads are writing to the data buffer while we're trying to
iterate over it. This will cause some lost stats, but no more than we're
currently losing to the app dying when it hits the race condition.
reddit_base: Fix incorrect "abort" import.

This was causing the fancy abort(SomeExceptionClass) style aborts to
fail because the pylons abort function didn't support that.