Move out-of-scope Arabian peninsula zones to 'backzone'.

* asia (Asia/Bahrain): Now links to Asia/Qatar.
(Asia/Kuwait, Asia/Aden): Now links to Asia/Riyadh.
(Asia/Muscat): Now links to Asia/Dubai.
* backzone: Move the old data here.
* checktab.awk (tztab): Remove special cases for these zones.
* NEWS: Document the above.

NEWS

@@ -8,6 +8,13 @@ Unreleased, experimental changes
     transition was Oct. 29, not Nov. 29.  Remove incorrect data from
     Shanks about time in Iceland between 1837 and 1908.
 
+    Some more zones have been turned into links, when they differed
+    from existing zones only for older time stamps.  As usual,
+    these changes affect UTC offsets in pre-1970 time stamps only.
+    Their old contents have been moved to the 'backzone' file.
+    The affected zones are: Asia/Aden, Asia/Bahrain, Asia/Kuwait,
+    and Asia/Muscat.
+
   Changes affecting code
 
     tzalloc now scrubs time zone abbreviations compatibly with the way

asia

@@ -145,10 +145,7 @@ Zone	Asia/Baku	3:19:24 -	LMT	1924 May  2
 			4:00	Azer	AZ%sT
 
 # Bahrain
-# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
-Zone	Asia/Bahrain	3:22:20 -	LMT	1920     # Manamah
-			4:00	-	GST	1972 Jun
-			3:00	-	AST
+# See Asia/Qatar.
 
 # Bangladesh
 # From Alexander Krivenyshev (2009-05-13):
@@ -1731,9 +1728,7 @@ Zone	Asia/Pyongyang	8:23:00 -	LMT	1908 Apr  1
 ###############################################################################
 
 # Kuwait
-# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
-Zone	Asia/Kuwait	3:11:56 -	LMT	1950
-			3:00	-	AST
+# See Asia/Riyadh.
 
 # Laos
 # See Asia/Bangkok.
@@ -1954,12 +1949,7 @@ Zone	Asia/Kathmandu	5:41:16 -	LMT	1920
 			5:45	-	NPT	# Nepal Time
 
 # Oman
-
-# Milne says 3:54:24 was the meridian of the Muscat Tidal Observatory.
-
-# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
-Zone	Asia/Muscat	3:54:24 -	LMT	1920
-			4:00	-	GST
+# See Asia/Dubai.
 
 # Pakistan
 
@@ -2453,6 +2443,7 @@ Zone	Asia/Manila	-15:56:00 -	LMT	1844 Dec 31
 Zone	Asia/Qatar	3:26:08 -	LMT	1920     # Al Dawhah / Doha
 			4:00	-	GST	1972 Jun
 			3:00	-	AST
+Link Asia/Qatar Asia/Bahrain
 
 # Saudi Arabia
 #
@@ -2479,6 +2470,8 @@ Zone	Asia/Qatar	3:26:08 -	LMT	1920     # Al Dawhah / Doha
 # Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
 Zone	Asia/Riyadh	3:06:52 -	LMT	1947 Mar 14
 			3:00	-	AST
+Link Asia/Riyadh Asia/Aden	# Yemen
+Link Asia/Riyadh Asia/Kuwait
 
 # Singapore
 # taken from Mok Ly Yng (2003-10-30)
@@ -2767,6 +2760,7 @@ Zone	Asia/Ashgabat	3:53:32 -	LMT	1924 May  2 # or Ashkhabad
 # Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
 Zone	Asia/Dubai	3:41:12 -	LMT	1920
 			4:00	-	GST
+Link Asia/Dubai Asia/Muscat	# Oman
 
 # Uzbekistan
 # Byalokoz 1919 says Uzbekistan was 4:27:53.
@@ -2851,10 +2845,4 @@ Zone Asia/Ho_Chi_Minh	7:06:40 -	LMT	1906 Jul  1
 			7:00	-	ICT
 
 # Yemen
-
-# Milne says 2:59:54 was the meridian of the saluting battery at Aden,
-# and that Yemen was at 1:55:56, the meridian of the Hagia Sophia.
-
-# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
-Zone	Asia/Aden	2:59:54	-	LMT	1950
-			3:00	-	AST
+# See Asia/Riyadh.

backzone

@@ -349,6 +349,17 @@ Zone Antarctica/McMurdo	0	-	zzz	1956
 			12:00	NZ	NZ%sT
 Link Antarctica/McMurdo Antarctica/South_Pole
 
+# Yemen
+# Milne says 2:59:54 was the meridian of the saluting battery at Aden,
+# and that Yemen was at 1:55:56, the meridian of the Hagia Sophia.
+Zone	Asia/Aden	2:59:54	-	LMT	1950
+			3:00	-	AST
+
+# Bahrain
+Zone	Asia/Bahrain	3:22:20 -	LMT	1920     # Manamah
+			4:00	-	GST	1972 Jun
+			3:00	-	AST
+
 # India
 #
 # From Paul Eggert (2014-09-06):
@@ -404,6 +415,16 @@ Zone	Asia/Kashgar	5:03:56	-	LMT	1928     # or Kashi or Kaxgar
 			5:00	-	KAST	1980 May
 			8:00	PRC	C%sT
 
+# Kuwait
+Zone	Asia/Kuwait	3:11:56 -	LMT	1950
+			3:00	-	AST
+
+
+# Oman
+# Milne says 3:54:24 was the meridian of the Muscat Tidal Observatory.
+Zone	Asia/Muscat	3:54:24 -	LMT	1920
+			4:00	-	GST
+
 # India
 # From Paul Eggert (2014-08-11), after a heads-up from Stephen Colebourne:
 # According to a Portuguese decree (1911-05-26)

checktab.awk

@@ -17,10 +17,6 @@ BEGIN {
 	if (zone_table == "zone1970.tab") {
 	  tztab["America/Antigua"] = 1
 	  tztab["America/Cayman"] = 1
-	  tztab["Asia/Aden"] = 1
-	  tztab["Asia/Bahrain"] = 1
-	  tztab["Asia/Kuwait"] = 1
-	  tztab["Asia/Muscat"] = 1
 	  tztab["Pacific/Midway"] = 1
 	  tztab["Pacific/Saipan"] = 1
 	}