[tz] Question about leap seconds

[Paul Eggert]

The practical point is that POSIX time can't represent leap seconds,
and that systems in practice get around this problems in various
ways, none of them standardized yet.

There is an effort underway to standardize this for RTP.
The draft says the POSIX clock jumps back at the start of
an inserted leap second; see

Gross K, van Brandeburg R.
RTP and Leap Seconds (2013-08-27)
http://tools.ietf.org/html/draft-ietf-avtcore-leap-second-04

But (as they mention) this definition doesn't match how well-regulated
POSIX clocks keep time in practice.  There was an earlier proposal
to standardize this:

Kuhn M.
Coordinated Universal Time with Smoothed Leap Seconds (UTC-SLS) (2006-01)
http://tools.ietf.org/html/draft-kuhn-leapsecond-00

but as far as I know, it has not been adopted in practice.