- Make query plan be re-saved after the first join execution
  (saving it after JOIN::cleanup is too late because EXPLAIN output 
   is currently produced before that)
- Handle QPF allocation/deallocation for edge cases, like unsuccessful
  BINLOG command.
- Work around the problem with UNION's direct subselects not being visible.
- Update test results ("Using temporary; Using filesort" are now always printed 
  last in the Extra column)
- This cset gets rid of memory leaks/crashes. Some result mismatches still remain.