[tz] tzcode-2014c breaks applications that use the binary tz files

[Paul Eggert]

Brian Inglis wrote:
> Given that all tz dates are in the Gregorian calendar

The tz code and database use the proleptic Gregorian calendar, which 
goes backwards in time before 1582, so we needn't do anything special 
with 1582 (or with 1867 for Alaskan timestamps, etc.).

There's a similar issue with seconds.  The current definition of the SI 
second wasn't clearly established until 1997, but we can and do extend 
it far backwards in time, as in the Big Bang estimate.