5th cut, moved DB related code to Event_db_repository and
updated accordingly the remanining code.
Moved change/restore_security_context() to class THD
Removed events_priv.h
Next step is to reorganize create/update_event() and parsing for them.
But probably some other refactoring could be done in the meanwhile.
The changes so far pass the test suite.


BitKeeper/deleted/.del-events_priv.h~2e8bce2cf35997df:
  Delete: sql/events_priv.h
sql/Makefile.am:
  events_priv.h is no more
sql/event_data_objects.cc:
  reorganize events code
sql/event_data_objects.h:
  reorganize events code
sql/event_db_repository.cc:
  reorganize events code
sql/event_db_repository.h:
  reorganize events code
sql/event_scheduler.cc:
  reorganize events code
sql/event_scheduler.h:
  reorganize events code
sql/events.cc:
  reorganize events code
sql/events.h:
  reorganize events code
sql/mysqld.cc:
  reorganize events code
sql/set_var.cc:
  reorganize events code
sql/sql_class.cc:
  add ::change_security_context() and restore_security_context()
sql/sql_class.h:
  add ::change_security_context() and restore_security_context()
sql/sql_db.cc:
  reorganize Events code
sql/sql_parse.cc:
  reorganize Events code
sql/sql_show.cc:
  reorganize Events code