Events were executed with all privileges possible on planet Earth :(
WL#1034


mysql-test/r/events.result:
  update test results
mysql-test/t/events.test:
  test for bug#17289 Events: missing privilege check for drop database
sql/event.h:
  -add two new methods to event_timed to change and restore
   the security context
sql/event_executor.cc:
  - move code regarding privilieges checking to event_timed::execute()
  - add a new function evex_print_warnings() which prints the notes/warnings/errors
    to the console (easily capturable with logs-into-tables) so one can see what
    has happened if there was an error of some sort!
sql/event_timed.cc:
  - fix documentation
  - add a new error code -99, EVENT was revoked from the user on the DB
  - set_sec_ctx, execute, restore_sex_ctx
sql/sql_error.cc:
  - make warning_level_names public to be used in event_executor.cc
  - change from 2 arrays to a LEX_STRING array