PLA-460 use left join to filter broken links

Don't merge. Just SQLReview.

@SQLReview 

mysql> explain SELECT page_len, page_id, page_title, rd_title, page_namespace, page_is_redirect FROM page IGNORE INDEX (`name_title`) LEFT JOIN redirect ON page_is_redirect = 1 AND page_id = rd_from LEFT JOIN querycache ON qc_title = page_title AND qc_type = 'BrokenRedirects' WHERE page_namespace IN (0) AND  (LOWER(page_title) LIKE 'john_pric%') AND ( qc_type IS NULL ) LIMIT 6;
+----+-------------+------------+--------+---------------+---------+---------+---------------------+--------+-------------------------+
| id | select_type | table      | type   | possible_keys | key     | key_len | ref                 | rows   | Extra                   |
+----+-------------+------------+--------+---------------+---------+---------+---------------------+--------+-------------------------+
|  1 | SIMPLE      | page       | ALL    | NULL          | NULL    | NULL    | NULL                | 149253 | Using where             |
|  1 | SIMPLE      | redirect   | eq_ref | PRIMARY       | PRIMARY | 4       | muppet.page.page_id |      1 |                         |
|  1 | SIMPLE      | querycache | ref    | qc_type       | qc_type | 32      | const               |      4 | Using where; Not exists |
+----+-------------+------------+--------+---------------+---------+---------+---------------------+--------+-------------------------+
3 rows in set (0.00 sec)