merge bug##7943: Wrong prefix lengths reported on UTF-8 columns

mysql-test/r/ctype_mb.result:
  Auto merged
sql/sql_show.cc:
  merge

mysql-test/r/ctype_mb.result

@@ -33,7 +33,7 @@ t1	CREATE TABLE `t1` (
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 SHOW KEYS FROM t1;
 Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment
-t1	1	key_a	1	a	A	NULL	9	NULL	YES	BTREE	
+t1	1	key_a	1	a	A	NULL	3	NULL	YES	BTREE	
 ALTER TABLE t1 CHANGE a a CHAR(4);
 SHOW CREATE TABLE t1;
 Table	Create Table
@@ -53,5 +53,5 @@ t1	CREATE TABLE `t1` (
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 SHOW KEYS FROM t1;
 Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment
-t1	1	key_a	1	a	A	NULL	9	NULL	YES	BTREE	
+t1	1	key_a	1	a	A	NULL	3	NULL	YES	BTREE	
 DROP TABLE t1;