BUG#16420: Events: timestamps become UTC

BUG#26429: SHOW CREATE EVENT is incorrect for an event that
           STARTS NOW()
BUG#26431: Impossible to re-create an event from backup if its
           STARTS clause is in the past
WL#3698: Events: execution in local time zone

The problem was that local times specified by the user in AT, STARTS
and ENDS of CREATE EVENT/ALTER EVENT statement were converted to UTC,
and the original time zone was forgotten.  This way, event scheduler
couldn't honor Daylight Saving Time shifts, and times shown to the
user were also in UTC.  Additionally, CREATE EVENT didn't allow times
in the past, thus preventing straightforward event restoration from
old backups.

This patch reworks event scheduler time computations, performing them
in the time zone associated with the event.  Also it allows times to
be in the past.

The patch adds time_zone column to mysql.event table.

NOTE: The patch is almost final, but the bug#9953 should be pushed
first.


client/mysqldump.c:
  Before every CREATE EVENT, output its time zone.
mysql-test/include/wait_condition.inc:
  Add optional $wait_timeout parameter.
mysql-test/lib/init_db.sql:
  Add time_zone column.
mysql-test/r/events.result:
  Update result.
mysql-test/r/events_bugs.result:
  Update result.
mysql-test/r/events_grant.result:
  Update result.
mysql-test/r/events_restart_phase1.result:
  Update result.
mysql-test/r/events_scheduling.result:
  Update result.
mysql-test/r/mysqldump.result:
  Update result.
mysql-test/r/ps.result:
  Update result.
mysql-test/r/system_mysql_db.result:
  Update result.
mysql-test/t/events.test:
  Remove STARTS from the result, as it depends on current time.
mysql-test/t/events_bugs.test:
  Time in the past is no longer an error.
mysql-test/t/events_restart_phase1.test:
  Fill new column 'time_zone' in mysql.event.
mysql-test/t/events_scheduling.test:
  Cleanup: disable event scheduler.
scripts/mysql_create_system_tables.sh:
  Add new column 'time_zone' to mysql.event.
scripts/mysql_fix_privilege_tables.sql:
  Add new column 'time_zone' to mysql.event.
sql/event_data_objects.cc:
  The essence of the change is the following:
   - for internal times use my_time_t instead of TIME.  Assignment and
     comparison is done now on plain numbers.
   - in init_execute_at(), init_starts(), init_ends() convert given time
     to number of seconds since Epoch (aka Unix time, in UTC).
   - handle time_zone field loading and storing.
   - in get_next_time(), Unix time is converted back to event time zone,
     interval is added, and the result is converted to UTC again.
   - fix Event_timed::get_create_event() to report STARTS and ENDS.
   - before executing the event body we set thread time zone to the
     event time zone.
sql/event_data_objects.h:
  Add time_zone member to Event_basic class.
  
  Store internal times in my_time_t (number of seconds since Epoch),
  rather than in broken down TIME structure.
sql/event_db_repository.cc:
  Add time_zone column handling.
  
  Give a warning and do not create an event if its execution time is in
  the past, and ON COMPLETION NOT PRESERVE is set, because such an event
  should be dropped by that time.  Also, do not allow ALTER EVENT to
  set execution time in the past when ON COMPLETION NOT PRESERVE is set.
sql/event_db_repository.h:
  Add enum member for new time zone column.
sql/event_queue.cc:
  Replace handling of broken down times with simple handling of
  my_time_t.
sql/event_queue.h:
  Store internal times in my_time_t (number of seconds since Epoch),
  rather than in broken down TIME structure.
sql/event_scheduler.cc:
  Add TODO comment.
sql/events.cc:
  Send time_zone column for SHOW CREATE EVENT.
sql/share/errmsg.txt:
  Update error message, and add two more errors.
sql/sql_show.cc:
  Add TIME_ZONE column to the output of SHOW EVENTS.
mysql-test/r/events_time_zone.result:
  BitKeeper file /home/tomash/src/mysql_ab/mysql-5.1-wl3698/mysql-test/r/events_time_zone.result
mysql-test/t/events_time_zone.test:
  BitKeeper file /home/tomash/src/mysql_ab/mysql-5.1-wl3698/mysql-test/t/events_time_zone.test

mysql-test/r/events_bugs.result

@@ -25,9 +25,12 @@ ERROR HY000: Incorrect STARTS value: '99990101000000'
 create event e_55 on schedule every 10 minute ends 99990101000000 do drop table t;
 ERROR HY000: ENDS is either invalid or before STARTS
 create event e_55 on schedule at 10000101000000 do drop table t;
-ERROR HY000: Activation (AT) time is in the past
+ERROR HY000: Incorrect AT value: '10000101000000'
 create event e_55 on schedule at 20000101000000 do drop table t;
-ERROR HY000: Activation (AT) time is in the past
+Warnings:
+Note	1584	Event execution time is in the past and ON COMPLETION NOT PRESERVE is set. Event has not been created
+show events;
+Db	Name	Definer	Time zone	Type	Execute at	Interval value	Interval field	Starts	Ends	Status
 create event e_55 on schedule at 20200101000000 starts 10000101000000 do drop table t;
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'starts 10000101000000 do drop table t' at line 1
 create event e_55 on schedule at 20200101000000 ends 10000101000000 do drop table t;