WL#1034 (Internal CRON)


mysql-test/r/events.result:
  add a test for to test bug #16431
mysql-test/t/events.test:
  results of new tests
sql/event.cc:
  - more debug info
  - pass info to evex_remove_from_cache() whether the operation 
    was drop or alter. this fixes possible bug that may lead to dropping
    of an event when it's altered. also fix for bug#16431
sql/event_executor.cc:
  be more verbose and throw more errors
sql/event_timed.cc:
  - add ` around the names of the db and the event_name and not
  their concatenation. remove ; from the end - unneeded. this fixes bug #16431,
  which was failing because after some recursion the query was ending on ;;
  which is normally an error in the parser because that's the delimiter
  
  - more debug info
  - don't execute lex_end() two times when there's a parse error or thd->is_fatal_error