fixed SLIVER_INFO time parsing

The original SLIVER_INFO code indirectly passed a datetime to mysql in RFC3339 format. That worked, on the old mysql version we were running.

But with a more recent mysql, things are more strict, and this doesn't work at all.

This fix uses POSIX::strftime("%Y-%m-%d %H:%M:%S", localtime(str2time($rfc3339_date_string))) to convert an RFC3339 date string to something that can be plugged directly into a mysql query. I hope that's correct? If there's a cleaner method, I'll change the code to that.