patch 8.1.0111: .po files do not use recommended names

Problem:    .po files do not use recommended names.
Solution:   Give a warning if the recommended name is not used.  Accept the
            recommended name for conversion. (Christian Brabandt, Ken Takata)
diff --git a/src/po/sjiscorr.c b/src/po/sjiscorr.c
index 2f55b9e..7aa0533 100644
--- a/src/po/sjiscorr.c
+++ b/src/po/sjiscorr.c
@@ -16,7 +16,8 @@
 	{
 		for (p = buffer; *p != 0; p++)
 		{
-			if (strncmp(p, "charset=utf-8", 13) == 0)
+			if (strncmp(p, "charset=utf-8", 13) == 0
+				|| strncmp(p, "charset=UTF-8", 13) == 0)
 			{
 				fputs("charset=cp932", stdout);
 				p += 12;