branches/5.1: Add reference to bug#47621 in the comment.

mysql-test/innodb-autoinc-44030.test

@@ -24,7 +24,7 @@ SELECT * FROM t1;
 # MySQL have made a change (http://lists.mysql.com/commits/75268) that no
 # longer results in the two data dictionaries being out of sync. If they
 # revert their changes then this check for ER_AUTOINC_READ_FAILED will need
-# to be enabled.
+# to be enabled. Also, see http://bugs.mysql.com/bug.php?id=47621.
 -- error ER_AUTOINC_READ_FAILED,1467
 INSERT INTO t1 VALUES(null);
 ALTER TABLE t1 AUTO_INCREMENT = 3;