- The reason the test failed was competition between 3+ QEPs with identical
  costs. Before, two plans were competing, and that was addressed by using 
  --sorted_result on the EXPLAIN output because they were different only in 
  join order.
  Now we've got a 3rd plan which differs with "Using where" and that doesn't 
  work anymore.
- This patch fixes it by removing 'Using where' from EXPLAIN output. Test coverage
  is somewhat reduced but probably still ok as PBXT and nested outer join processing
  have no interaction and we don't expect any bugs here.