[tz] [PROPOSED] Fix off-by-1 error for Jamaica and T&C before 1913

[Paul Eggert]

This was discovered when checking a not-yet-published
version of zic.
* NEWS: Mention this.
* northamerica (America/Jamaica, America/Grand_Turk):
* backzone (America/Cayman): Fix rounding error.
---
 NEWS         | 3 +++
 backzone     | 2 +-
 northamerica | 6 +++---
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/NEWS b/NEWS
index beefd39..f00b29f 100644
--- a/NEWS
+++ b/NEWS
@@ -11,6 +11,9 @@ Unreleased, experimental changes
     Enderbury and Kiritimati skipped New Year's Eve 1994, not
     New Year's day 1995.  (Thanks to Kerry Shetline.)
 
+    Fix an off-by-1 error for pre-1913 timestamps in Jamaica and in
+    Turks & Caicos.
+
   Changes to build procedure
 
     The new XDST macro in the Makefile lets the installer choose
diff --git a/backzone b/backzone
index 3006b27..cc724aa 100644
--- a/backzone
+++ b/backzone
@@ -271,7 +271,7 @@ Zone	America/Aruba	-4:40:24 -	LMT	1912 Feb 12 # Oranjestad
 
 # Cayman Is
 Zone	America/Cayman	-5:25:32 -	LMT	1890     # Georgetown
-			-5:07:11 -	KMT	1912 Feb # Kingston Mean Time
+			-5:07:10 -	KMT	1912 Feb # Kingston Mean Time
 			-5:00	-	EST
 
 # Canada
diff --git a/northamerica b/northamerica
index a014126..dabca97 100644
--- a/northamerica
+++ b/northamerica
@@ -3264,8 +3264,8 @@ Zone America/Tegucigalpa -5:48:52 -	LMT	1921 Apr
 # http://www.jamaicaobserver.com/columns/The-politician-in-all-of-us_17573647
 #
 # Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
-Zone	America/Jamaica	-5:07:11 -	LMT	1890        # Kingston
-			-5:07:11 -	KMT	1912 Feb    # Kingston Mean Time
+Zone	America/Jamaica	-5:07:10 -	LMT	1890        # Kingston
+			-5:07:10 -	KMT	1912 Feb    # Kingston Mean Time
 			-5:00	-	EST	1974
 			-5:00	US	E%sT	1984
 			-5:00	-	EST
@@ -3415,7 +3415,7 @@ Zone America/Miquelon	-3:44:40 -	LMT	1911 May 15 # St Pierre
 #
 # Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
 Zone America/Grand_Turk	-4:44:32 -	LMT	1890
-			-5:07:11 -	KMT	1912 Feb # Kingston Mean Time
+			-5:07:10 -	KMT	1912 Feb # Kingston Mean Time
 			-5:00	-	EST	1979
 			-5:00	US	E%sT	2015 Nov Sun>=1 2:00
 			-4:00	-	AST	2018 Mar 11 3:00
-- 
2.14.3