the C library, internally) for all kinds of date calculations based
on the Gregorian calendar (the one used in all western countries today),
thereby complying with all relevant norms and standards: ISO/R 2015-1971,
DIN 1355 and, to some extent, ISO 8601 (where applicable).
PR: 16979
Submitted by: Brad Hendrickse <bradh@uunet.co.za>