Fix Louisville spring-forward in 1946 and 1950

Problem reported by Alois Triendl in:
https://mm.icann.org/pipermail/tz/2019-August/028401.html
* NEWS: Mention this.
* northamerica (Louisville): Fix errors in transcribing
data from Shanks.

NEWS

@@ -33,6 +33,10 @@ Unreleased, experimental changes
     EET/EEST, not CET/CEST.  (Thanks to Alois Triendl.)  In 1946
     Königsberg switched to +03 on 04-07 not 01-01.
 
+    In 1946 Louisville switched from CST to CDT on 04-28, not 01-01.
+    (Thanks to Alois Treindl.)  Also, it switched from CST to CDT
+    on 1950-04-30, not 1947-04-27.
+
   Changes to past time zone abbreviations and DST flags
 
     Hong Kong Winter Time, observed from 1941-10-01 to 1941-12-25,

northamerica

@@ -1065,11 +1065,13 @@ Zone America/Indiana/Vevay -5:40:16 -	LMT	1883 Nov 18 12:19:44
 # Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE	LETTER
 Rule Louisville	1921	only	-	May	1	2:00	1:00	D
 Rule Louisville	1921	only	-	Sep	1	2:00	0	S
-Rule Louisville	1941	1961	-	Apr	lastSun	2:00	1:00	D
+Rule Louisville	1941	only	-	Apr	lastSun	2:00	1:00	D
 Rule Louisville	1941	only	-	Sep	lastSun	2:00	0	S
+Rule Louisville	1946	only	-	Apr	lastSun	2:00	1:00	D
 Rule Louisville	1946	only	-	Jun	2	2:00	0	S
+Rule Louisville	1950	1961	-	Apr	lastSun	2:00	1:00	D
 Rule Louisville	1950	1955	-	Sep	lastSun	2:00	0	S
-Rule Louisville	1956	1960	-	Oct	lastSun	2:00	0	S
+Rule Louisville	1956	1961	-	Oct	lastSun	2:00	0	S
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
 Zone America/Kentucky/Louisville -5:43:02 -	LMT	1883 Nov 18 12:16:58
 			-6:00	US	C%sT	1921