make/data/tzdata/leapseconds

8216178: (tz) Upgrade time-zone data to tzdata2018i
Reviewed-by: duke

@@ -1,28 +1,5 @@
-#
-# DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
-#
-# This code is free software; you can redistribute it and/or modify it
-# under the terms of the GNU General Public License version 2 only, as
-# published by the Free Software Foundation.  Oracle designates this
-# particular file as subject to the "Classpath" exception as provided
-# by Oracle in the LICENSE file that accompanied this code.
-#
-# This code is distributed in the hope that it will be useful, but WITHOUT
-# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
-# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
-# version 2 for more details (a copy is included in the LICENSE file that
-# accompanied this code).
-#
-# You should have received a copy of the GNU General Public License version
-# 2 along with this work; if not, write to the Free Software Foundation,
-# Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
-#
-# Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
-# or visit www.oracle.com if you need additional information or have any
-# questions.
-#
 # Allowance for leap seconds added to each time zone file.
 
 # This file is in the public domain.
 
 # This file is generated automatically from the data in the public-domain

@@ -40,13 +17,16 @@
 # and publishes leap second data in a copyrighted file
 # <https://hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat>.
 # See: Levine J. Coordinated Universal Time and the leap second.
 # URSI Radio Sci Bull. 2016;89(4):30-6. doi:10.23919/URSIRSB.2016.7909995
 # <https://ieeexplore.ieee.org/document/7909995>.
+
 # There were no leap seconds before 1972, because the official mechanism
 # accounting for the discrepancy between atomic time and the earth's rotation
-# did not exist.
+# did not exist.  The first ("1 Jan 1972") data line in leap-seconds.list
+# does not denote a leap second; it denotes the start of the current definition
+# of UTC.
 
 # The correction (+ or -) is made at the given time, so lines
 # will typically look like:
 #       Leap    YEAR    MON     DAY     23:59:60        +       R/S
 # or