+PH/20 Added macros for time_t as for off_t (see PH/15 above) and used them to
+ rework some of the code of TK/09 above to avoid the hardwired use of
+ "%lld" and "long long". Replaced the call to snprintf() with a call to
+ string_vformat().
+
+PH/21 Added another message to those in 4.51/PH/42, namely "All relevant MX
+ records point to non-existent hosts".
+