Comment 2 for bug 727667

This is 5.2, for comparison:
MariaDB [j28]> explain SELECT * FROM t1 WHERE (f3 = 83) OR (f10 = 'z' AND f3 IS NULL);
+----+-------------+-------+-------------+---------------+------+---------+-------+------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------------+---------------+------+---------+-------+------+-------------+
| 1 | SIMPLE | t1 | ref_or_null | f3 | f3 | 5 | const | 2 | Using where |
+----+-------------+-------+-------------+---------------+------+---------+-------+------+-------------+
1 row in set (0.00 sec)