Fixed race condition in event that could cause hang when stopping event scheduler with SET GLOBAL event_scheduler=OFF 

client/mysqltest.cc:
  Write command to be executed to the log BEFORE executing the command.
  This makes it easier to debug crashes as the log will contain the fatal command.
mysql-test/r/mysqltest.result:
  Updated results (we now get more things logged)
sql/event_queue.cc:
  Fixed race condition in event that could cause hang when stopping event scheduler with SET GLOBAL event_scheduler=OFF.
  The reason was that a kill signal could be sent between last check of thd->killed and before thd->enter_cond() in which case the signal
  would be missed and we would be stuck in Event_scheduler::stop() forever.