[tz] [PROPOSED 2/3] Simplify leapadd

[Paul Eggert]

On 1/14/20 7:04 PM, Steve Allen wrote:
> the original draft of CCIR Recommendation 460
> allowed for leaps of "integral multiples" of one second.

Ah, I didn't know that. Still, the 1989 C standard botched this, since C89 
allowed for leaps of one or two (but no more) seconds, apparently on the 
mistaken assumption that that could have happened under the then-current leap 
second rules. And this botch was copied into POSIX.

Although the two-leap-second botch was fixed in the C99 and POSIX-2001 
standards, it was still present (though with bugs) in tzcode until the buggy 
support was removed in tzcode 2017c.