(cleanups, leaks fixed)


sql/event.cc:
  - update comments
  - remove dead code
  - event_timed is no more copied after allocation on a DYNAMIC_ARRAY
    because there is a problem when the array is reallocated - we get
    dangling pointers from the scheduling queue. anyway it makes little
    sense to keep them there except that cleaning is quite efficient but
    iterating over all events and cleaning them one by one is not that bad
    considering that happens only when the main scheduler thread is killed
    or during server shutdown.
sql/event_executor.cc:
  - DYNAMIC_ARRAY is no more
sql/event_priv.h:
  - remove unneeded code/defines. the scheduler's queue is of 
    type QUEUE and cannot run anymore on top of DYNAMIC_ARRAY
sql/event_timed.cc:
  - after parsing (in ::compile() ) destruct the event_timed object
sql/sql_parse.cc:
  in case of syntax error clean up lex->et because there could be an object
  created. as in the code the same is done for SPs.