new features:
set event_scheduler=ON|OFF will now try to init event scheduler
if it's not enabled
set event_scheduler=default will try to enable it based on
the value of the event_scheduler when mysqld was started
in mysql_upgrade: do FLUSH PRIVILEGES at the end, not together with
mysql_fix_privilege_tables
mysql-test/t/mysql_upgrade-6984.opt:
use a dummy second option to force server restart after the test
