HKWT observed in late 1941 in Hong Kong

* NEWS: Mention this.
* asia (Asia/Hong_Kong): Treat the period from 1941-10-01 to
1941-12-25 as 30-minute DST rather than as standard time.
* theory.html (Time zone abbreviations): Add HKWT.

NEWS

@@ -12,6 +12,11 @@ Unreleased, experimental changes
     Fix several errors in pre-1970 transitions in Perry County, IN.
     (Thanks to Alois Triendl for pointing out the 1967/9 errors.)
 
+  Changes to past time zone abbreviations and DST flags
+
+    Hong Kong Winter Time, observed from 1941-10-01 to 1941-12-25,
+    is now flagged as DST and is abbreviated HKWT not HKT.
+
   Changes to commentary
 
     Nashville's newspapers dueled about the time of day in the 1950s.

asia

@@ -8,7 +8,7 @@
 # [email protected] for general use in the future).  For more, please see
 # the file CONTRIBUTING in the tz distribution.
 
-# From Paul Eggert (2018-06-19):
+# From Paul Eggert (2019-07-11):
 #
 # Unless otherwise specified, the source for data through 1990 is:
 # Thomas G. Shanks and Rique Pottenger, The International Atlas (6th edition),
@@ -47,13 +47,13 @@
 #	7:00 WIB	west Indonesia (Waktu Indonesia Barat)
 #	8:00 WITA	central Indonesia (Waktu Indonesia Tengah)
 #	8:00 CST	China
-#	8:00 PST  PDT*	Philippine Standard Time
+#	8:00 HKT  HKST	Hong Kong (HKWT* for Winter Time in late 1941)
+#	8:00 PST  PDT*	Philippines
 #	8:30 KST  KDT	Korea when at +0830
 #	9:00 WIT	east Indonesia (Waktu Indonesia Timur)
 #	9:00 JST  JDT	Japan
 #	9:00 KST  KDT	Korea when at +09
-#	9:30 ACST	Australian Central Standard Time
-# *I invented the abbreviation PDT; see "Philippines" below.
+# *I invented the abbreviations HKWT and PDT; see below.
 # Otherwise, these tables typically use numeric abbreviations like +03
 # and +0330 for integer hour and minute UT offsets.  Although earlier
 # editions invented alphabetic time zone abbreviations for every
@@ -653,6 +653,15 @@ Zone	Asia/Urumqi	5:50:20	-	LMT	1928
 # * 1941-09-30, Hong Kong Daily Press, Winter Time Warning.
 #   https://i.imgur.com/dge4kFJ.png
 
+# From Paul Eggert (2019-07-11):
+# "Hong Kong winter time" is considered to be daylight saving.
+# "Hong Kong had adopted daylight saving on June 15 as a wartime measure,
+# clocks moving forward one hour until October 1, when they would be put back
+# by just half an hour for 'Hong Kong Winter time', so that daylight saving
+# operated year round." -- Low Z. The longest day: when wartime Hong Kong
+# introduced daylight saving. South China Morning Post. 2019-06-28.
+# https://www.scmp.com/magazines/post-magazine/short-reads/article/3016281/longest-day-when-wartime-hong-kong-introduced
+
 # From P Chan (2018-12-31):
 # * According to the Hong Kong Daylight-Saving Regulations, 1941, the
 #   1941 spring-forward transition was at 03:00.
@@ -754,7 +763,7 @@ Rule	HK	1979	only	-	Oct	21	3:30	0	-
 Zone	Asia/Hong_Kong	7:36:42 -	LMT	1904 Oct 30  0:36:42
 			8:00	-	HKT	1941 Jun 15  3:00
 			8:00	1:00	HKST	1941 Oct  1  4:00
-			8:30	-	HKT	1941 Dec 25
+			8:00	0:30	HKWT	1941 Dec 25
 			9:00	-	JST	1945 Nov 18  2:00
 			8:00	HK	HK%sT
 

theory.html

@@ -428,7 +428,7 @@ <h2 id="abbreviations">Time zone abbreviations</h2>
       EET/EEST Eastern European,
       GST/GDT Guam,
       HST/HDT/HWT/HPT Hawaii,
-      HKT/HKST Hong Kong,
+      HKT/HKST/HKWT Hong Kong,
       IST India,
       IST/GMT Irish,
       IST/IDT/IDDT Israel,