Cut number 6. Move code from sql_show.cc to event_db_repository.cc
that more belongs to the latter.


sql/event_db_repository.cc:
  move code that works with mysql.event from sql_show.cc to 
  event_db_repository.cc . Route through Event_db_repository's interface
  which is proxied by class Events. The code relies on a function from
  sql_show.cc which does the actual storage in the schema table. I think
  it's better to leave the function there because the structure of 
  I_S.EVENTS is defined in sql_show.cc
sql/event_db_repository.h:
  I_S / SHOW EVENTS handling hooks
sql/event_scheduler.cc:
  use the pointer to db_repository which Event_scheduler already has
sql/events.cc:
  Put a comment to get_instance
sql/events.h:
  callback for I_S (sql_show.cc)
sql/sql_show.cc:
  move code that belongs more to Event_db_repository than to here.
  Use a callback of class Events. Only 1 function is left here, because
  it copies data into the actual rows of I_S.EVENTS and belongs to this file.
sql/sql_show.h:
  export this function will be called from event_db_repository.cc