[tz] Fractional seconds in zic input

[Paul Eggert]

On 02/05/2018 09:34 AM, John Hawkinson wrote:
> Regardless of whether it was labelled "experimental" or "mainline" or "development," the fact is that it is the source from which releases are cut.

Yes, as tz-link.html says, the GitHub repository is a development 
repository. Its latest version is always intended to be suitable for 
release on pretty much a moment's notice (since governments often don't 
give us much notice); this was true even when the GitHub repository was 
called "experimental".

None of the recently-installed changes were intended to depart from this 
procedure. The only changes since 2018c that affect the data are 
relatively routine: they are a 1-day correction to Kiribati's 
change-of-day in 1994/5, and a 1-second correction to Jamaica etc. 
before 1913. In the code there is also a porting fix for macOS awk that 
to my mind is the most-important change that would prompt a new release. 
Although other recently-installed changes are significant, they are 
important only for future releases, not for the current development code 
or data as used by current downstream packages.

Although we could change tzdata in the future, these are changes that 
haven't been installed into the development version, or even proposed in 
detail as patches. If and when they are made, they should be accompanied 
by a procedure that continues to generate data in the current format, a 
draft of which is in the repository now.