Allow fixing timestamps that miss the year

[fxnn]

Turns out that Syslog doesn't log the year.

Apr  5 05:39:01 lvps176-28-9-153 CRON[5773]: pam_unix(cron:session): session opened for user root by (uid=0)

Looks like we need to calculate the date. We could do this

• using the timestamp of the logfile itself, or
• using our current datetime, assuming the year is either the current year or, if the timestamp would be in future then, the year before.