pg_audit_users - Auditing user activity

Hi

I'm working on a web credit card payment solution, so in a PCI-DSS environment,
and the auditors gave me trouble with one specific audit point for the
PostgreSQL database. They require the list of users in the database that had no
activity in the past 90 days to be deleted.
So far, it seems the only solution to implement that in PostgreSQL would be to
parse the log, hoping not to lose any line.
That seems too risky for me, so I wrote my own solution for this issue, and I
would like to submit it here for review/suggestion and to help other users
facing the same needs. Since it's very small, I've taken the liberty of
attaching it to this email.
The code is more or less «inspired» by pg_stat_statements. So far I've not
implemented saving upon restarts of the database, I'll probably do it in the
next days/weeks. It has been tested against PostgreSQL 9.2 only, but I'll test
9.3 and 9.4 soon.

Thanks

Pierre