fix up database update and backfill script to work with higher accuracy

After seeing this in action on the production database, I have made a few tweaks.

Once this is live, I would like to adjust the cron job to run backfill_regressions.py after updatedb.py.

After that is in place, I will need to add a html page to the static/ folder outlining how to use the api, and probably include an example script or two for analyzing data.