Correct China DST transitions in 1986/91

(Thanks to P Chan.)
* NEWS: Mention this.
* asia (PRC): Change AT column from 00:00 to 02:00.
Change 1987/91 rule from Apr Sun>=10 to Apr Sun>=11, so that
the 1988 transition is on April 17, not April 10.

NEWS

@@ -7,6 +7,10 @@ Unreleased, experimental changes
     The 2018-05-05 North Korea 30-minute time zone change took place
     at 23:30 the previous day, not at 00:00 that day.
 
+    China's 1988 spring-forward transition was on May 17, not May 10.
+    Its DST transitions in 1986/91 were at 02:00, not 00:00.  (Thanks
+    to P Chan.)
+
   Changes to build procedure
 
     New 'make' target 'rearguard_tarballs' to build the rearguard

asia

@@ -307,18 +307,36 @@ Zone	Asia/Yangon	6:24:47 -	LMT	1880        # or Rangoon
 # time - sort of", Los Angeles Times, 1986-05-05 ... [says] that China began
 # observing daylight saving time in 1986.
 
-# From Paul Eggert (2014-06-30):
-# Shanks & Pottenger have China switching to a single time zone in 1980, but
-# this doesn't seem to be correct.  They also write that China observed summer
-# DST from 1986 through 1991, which seems to match the above commentary, so
-# go with them for DST rules as follows:
+# From P Chan (2018-05-07):
+# The start and end time of DST in China [from 1986 on] should be 2:00
+# (i.e. 2:00 to 3:00 at the start and 2:00 to 1:00 at the end)....
+# Government notices about summer time:
+#
+# 1986-04-12 http://www.zj.gov.cn/attach/zfgb/198608.pdf p.21-22
+# (To establish summer time from 1986. On 4 May, set the clocks ahead one hour
+# at 2 am. On 14 September, set the clocks backward one hour at 2 am.)
+#
+# 1987-02-15 http://www.gov.cn/gongbao/shuju/1987/gwyb198703.pdf p.114
+# (Summer time in 1987 to start from 12 April until 13 September)
+#
+# 1987-09-09 http://www.gov.cn/gongbao/shuju/1987/gwyb198721.pdf p.709
+# (From 1988, summer time to start from 2 am of the first Sunday of mid-April
+# until 2 am of the first Sunday of mid-September)
+#
+# 1992-03-03 http://www.gov.cn/gongbao/shuju/1992/gwyb199205.pdf p.152
+# (To suspend summer time from 1992)
+#
+# The first page of People's Daily on 12 April 1988 stating that summer time
+# to begin on 17 April.
+# http://data.people.com.cn/pic/101p/1988/04/1988041201.jpg
+
 # Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE	LETTER/S
 Rule	Shang	1940	only	-	Jun	 3	0:00	1:00	D
 Rule	Shang	1940	1941	-	Oct	 1	0:00	0	S
 Rule	Shang	1941	only	-	Mar	16	0:00	1:00	D
-Rule	PRC	1986	only	-	May	 4	0:00	1:00	D
-Rule	PRC	1986	1991	-	Sep	Sun>=11	0:00	0	S
-Rule	PRC	1987	1991	-	Apr	Sun>=10	0:00	1:00	D
+Rule	PRC	1986	only	-	May	 4	2:00	1:00	D
+Rule	PRC	1986	1991	-	Sep	Sun>=11	2:00	0	S
+Rule	PRC	1987	1991	-	Apr	Sun>=11	2:00	1:00	D
 
 # From Anthony Fok (2001-12-20):
 # BTW, I did some research on-line and found some info regarding these five