Correctly handle serving only a single list
Make sure we disable backoff fuzzing in mozsvc tweens
S3 single file source support

And some tweaks to shavar.tests.base to minimize code duplication
Address various nits from PR 18
Add support for testing S3 decision logic

Add test to exercise source URL decision logic in
shavar.lists.SafeBrowsingList.__init__
Merge pull request #18 from rtilder/rtilder/s3-file-source

Add basic S3 source support, so we can get this out to stage for further testing