make more independent of SP


sql/event.cc:
  use own routine - export it
sql/event_priv.h:
  export these two
sql/event_timed.cc:
  use own routine, don't rely on SP
sql/sp.cc:
  revert changes to SP
sql/sp.h:
  revert changes to SP
sql/sql_show.cc:
  rever changes to SP