Say an account without its time as age unknown, not as two thousand years (issue 160)

cmd/mesh-controller/machine_lines.go

@@ -24,7 +24,12 @@ func machineLines(a inventory.MachineAccount, had bool, now time.Time) []string
 			"    " + factLine("kernel", orUnsaid(a.Kernel)),
 		}
 	}
-	out := []string{fmt.Sprintf("  what it is made of, as it said %s ago:", roughly(now.Sub(m.ObservedAt)))}
+	age := roughly(now.Sub(m.ObservedAt)) + " ago"
+	if m.ObservedAt.IsZero() {
+		// Said with no time: its age is not known, and is never read as two thousand years.
+		age = "at a time it did not say (age unknown)"
+	}
+	out := []string{fmt.Sprintf("  what it is made of, as it said %s:", age)}
 	add := func(name, value string) { out = append(out, "    "+factLine(name, value)) }
 	unknown := map[string]string{}
 	for k, v := range m.Unknown {