Re: I don't see what the fuss is about
So the conversion routines will now need to know about and account for the new leap second? And all those old Unixes unaware of it will be off one second?
You are wrong on both accounts. Firstly you have to understand the various concepts of "time" that are in use, and that suggests you don’t. We have:
Calendar time, this is what time_t and similar operates upon and what most people think of, and here each day ALWAYS has 60*60*24 = 86400 seconds, and the calculation of date is based upon the Gregorian calendar for leap years. The application of leap seconds has absolutely no impact upon such calculations, in effect it is just a step adjustment of time-of-day to keep it within 1 second of mean solar time as defined from the Earth's rotation and orbit. The difference in time between points is computed ignoring leap seconds, so it is actually "wrong" if you need an accurate time difference across such an event.
Ephemeris time and all of its variants (GPS time, TDT, etc) where you have some defined epoch and time is measured in fixed seconds based on atomic time from that point. Each of such systems has no leap seconds and no discontinuities, so time differences are always right. However, to equate such a linear time to calendar time you do need to know the history of leap seconds and for that you would need a table of data. For web-connected machines you can get it from here along with the finer details of the Earth's orientation:
Finally this is exactly the same for any OS, it is just that historically UNIX has handled time in a sane and correct manner (e.g. system clock on UTC, NTP adjustment slewing time normally to avoids steps and to minimise the error w.r.t several time servers, NTP signalling leap seconds before they occur, etc) even if code monkeys sometimes get it wrong. However windows has had pretty poor ways of doing things (e.g. CMOS clock keeping local daylight-adjusted time, time steps once per week by default based on just the MS time server to keep the lock within minutes of correct time, etc).