Cleaned up the code a bit. Fixed few leaks.
This code still does not load events on server startup
from disk. The problem is that there is a need for a THD instance, which
does not exist during server boot. This will be solved soon.
Still Event_timed is used both for the memory queue and for exectution.
This will be changed according to WL#3337 probably in the next commit.


sql/event_data_objects.cc:
  Strip unneeded stuff from class Event_timed
  Event_timed is still used for the queue and execution.
  That will be changed in the next commit.
sql/event_data_objects.h:
  Strip unneeded stuff from class Event_timed
  Event_timed is still used for the queue and execution.
  That will be changed in the next commit.
sql/event_db_repository.cc:
  Cosmetics.
  Add a new method load_named_event_job, to be made complete in the 
  next commit. It will load from disk an instance of Event_job_data to
  be used during execution.
sql/event_db_repository.h:
  find_event does not need MEM_ROOT anymore
  because the memory is allocated on Event's own root.
sql/event_queue.cc:
  Remove dead code.
  Move dumping of the queue to separate method.
  Make critical sections in create_event & update_event
  as small as possible - load the new event outside of the section
  and free the object also outside of it.
sql/event_queue.h:
  init -> init_queue -> easier for ctags
  deinit -> deinit_queue -> easier for ctags
sql/event_scheduler.cc:
  empty this file
sql/event_scheduler.h:
  empty this file
sql/event_scheduler_ng.cc:
  add back DBUG_RETURN(0) in thread handlers.
  We don't stop running events when stopping the scheduler. Therefore
  remove this method now. If it is needed later it can be added back.
sql/event_scheduler_ng.h:
  Remove stop_all_running_threads()
  init -> init_scheduler
  deinit -> deinit_scheduler
  easier for ctags
sql/events.cc:
  Cosmetics
sql/events.h:
  Cosmetics
sql/set_var.cc:
  Remove references to dead code
sql/sql_parse.cc:
  Reorganize a bit.