- In mi_rkey(), do correct handling of case where mi_yield_and_check_if_killed() 
  detects that the thread was killed (all other similar functions in MyISAM/Aria have 
  slightly different code and do not have this problem).
- Also fixed assignment in DBUG_ASSERT
- this is 2nd variant of the fix:
   = make .result file smaller
   = run KILLable statements in a separate connection, otherwise we could end up trying to 
     KILL the final "DROP TABLE" statement