[tz] tzfiles contain Unix epoch for the first transition time

[Paul Eggert]

Robert Elz wrote:
> After I sent the last message, I wondered if perhaps the system Eric
> used represented times in (fixed point) Java type notation, in milliseconds
> since the epoch, rather than seconds - but even with that form, the big
> bang timestamp doesn't overflow 64 bits

Microsoft file times are unsigned 64-bit quantities that count the number of 
100ns intervals since 1601-01-01 00:00:00 universal time.  If his system is 
using this format, that'd explain why it overflows for the Big Bang -- though it 
wouldn't explain why the result was dated 1970.