send_status on exists records
Adding audit_period_beginning/ending to exists table
Adding missing indexes on usage data
Using audit_period_ending in _verify_for_delete

The previous logic used the raw's timestamp, which could end up
    slightly outside of the audit period. This would give us a
    small window where a delete could happen outside of the
    audit period, but we'd still detect it. The new logic uses
    the exact end of the audit period.
Merge pull request #60 from ramielrowe/exists_audit_period

audit_period_beginning/ending and send_status on exists records