Merge pull request #809 from slingamn/graceperiod

fix handling of history grace periods

irc/server.go

 	}
 	if config.History.Restrictions.EnforceRegistrationDate {
 		regCutoff := client.historyCutoff()
-		regCutoff.Add(-time.Duration(config.History.Restrictions.GracePeriod))
-		// take the earlier of the two cutoffs
+		// take the later of the two cutoffs
 		if regCutoff.After(cutoff) {
 			cutoff = regCutoff
 		}
 	}
+	if !cutoff.IsZero() {
+		cutoff = cutoff.Add(-time.Duration(config.History.Restrictions.GracePeriod))
+	}
 	if hist != nil {
 		sequence = hist.MakeSequence(recipient, cutoff)
 	} else if recipient != "" {