This is a post-review patch.

Fixes the typelib implementation, available only in 5.1.11.

--event-scheduler cmdline : DISABLED | ON | OFF | 0 | 1
DISABLED - makes the scheduler unavailable during the server run
(ON|1)-  When the server is started the scheduler will be started. It can
         be stopped and restarted by setting appropriate values to
         GLOBAL event_scheduler
(OFF|0)- When the server is started, the scheduler won't be started. It
         can be started and again stopped by setting appropriate values to
         GLOBAL event_scheduler. _DEFAULT_ value

The GLOBAL variable event_scheduler can have the following values:
OFF | ON | 0 | 1
DISABLED is not possible and every attempt will end with an error that
it's not a valid value for the variable.
OFF | 0 - This is the pre-5.1.11 behavior - The scheduler stops, if not
          already stopped, and can be started again  by setting
          the value of the variable to ON|1.
ON | 1  - This is the pre-5.1.11 behavior - The scheduler starts, if not
          already started, and can be stopped again by setting the value
          of the variable to OFF|0.


mysql-test/r/events.result:
  update result
mysql-test/r/events_bugs.result:
  update result
mysql-test/r/events_logs_tests.result:
  update result
mysql-test/r/events_restart_phase1.result:
  update result
mysql-test/r/events_restart_phase3.result:
  update result
mysql-test/r/events_scheduling.result:
  update result
mysql-test/r/events_stress.result:
  update result
mysql-test/t/events.test:
  update test:
  2 -> off
  1 -> on
mysql-test/t/events_bugs.test:
  update test:
  2 -> off
  1 -> on
mysql-test/t/events_logs_tests.test:
  update test:
  2 -> off
  1 -> on
mysql-test/t/events_restart_phase1.test:
  update test:
  2 -> off
  1 -> on
mysql-test/t/events_restart_phase2-master.opt:
  update master file : 1 => on
mysql-test/t/events_scheduling.test:
  update test:
  2 -> off
  1 -> on
  
  add tests for event_scheduler global variable representation from
  SHOW VARIABLES.
mysql-test/t/events_stress.test:
  update test:
  2 -> off
  1 -> on
sql/events.cc:
  Implement two different TYPELIBs for --event-scheduler cmd line
  option and for GLOBAL variable event_scheduler
  
  --event-scheduler cmdline : DISABLED | ON | OFF | 0 | 1
  DISABLED - makes the scheduler unavailable during the server run
  (ON|1)-  When the server is started the scheduler will be started. It can
           be stopped and restarted by setting appropriate values to
           GLOBAL event_scheduler
  (OFF|0)- When the server is started, the scheduler won't be started. It
           can be started and again stopped by setting appropriate values to
           GLOBAL event_scheduler. _DEFAULT_ value
  
  The GLOBAL variable event_scheduler can have the following values:
  OFF | ON | 0 | 1
  DISABLED is not possible and every attempt will end with an error that
  it's not a valid value for the variable.
  OFF | 0 - This is the pre-5.1.11 behavior - The scheduler stops, if not
            already stopped, and can be started again  by setting
            the value of the variable to ON|1.
  ON | 1  - This is the pre-5.1.11 behavior - The scheduler starts, if not
            already started, and can be stopped again by setting the value
            of the variable to OFF|0.
sql/events.h:
  additional TYPELIB for GLOBAL event_scheduler
sql/mysqld.cc:
  --event-scheduler should be checked against a TYPELIB and
  therefore should be GET_STR, as well as we make the parameter optional.
  When not provided OFF|0 is used.
sql/set_var.cc:
  Implement typelib for event_scheduler variable.
  If allows both INT_RESULT -> 0 | 1 
  and STRING_RESULT -> OFF | ON
  The variable is shown as DISABLED | ON | OFF
sql/set_var.h:
  Implement typelib, which expects both STRING and INT,
  for event_scheduler.