QUEUE implementation working now. this should be ready more or less
for testing once the debug output is being cleaned and some things
around DYNAMIC_ARRAY are cleaned
- fix handling in case of errors that lead to crashes, now no more crashes
  in case of table corruption and such.


include/queues.h:
  introduce a safe version of queue_insert that will extend the queue if
  necessary. the auto_extent is passed to the _ex version of init_queue()
mysys/queues.c:
  add init_queue_ex() implementation
  add queue_insert_safe() implementation
sql/event.cc:
  - move mysql_priv.h inclusion to event_priv.h
  - use a priority queue instead of DYNAMIC_ARRAY which is sorted
sql/event.h:
  reorder
sql/event_executor.cc:
  reorder
sql/event_priv.h:
  - reorder a bit
  - add macroses and functions for queue manipulation which stay on top
   of QUEUE (partly implemented for DYNAMIC_ARRAY but will be cleared to be
   only for QUEUE).
sql/event_timed.cc:
  allocate one more byte and zeroterminate, really