sql/sp.cc:
  don't split "user@host" string in db_load_routine, because the caller needs to
  generate it from user and host. instead pass user and host directly into db_load_routine
sql/sql_parse.cc:
  1. REVOKE ALL doesn't need invoker.
  2. make sp_process_definer() reusable
sql/sql_trigger.cc:
  don't duplicate the code from sp_process_definer(), reuse it
sql/sql_view.cc:
  don't duplicate the code from sp_process_definer(), reuse it