Fixed crash on double free when exiting.

The key of hash table item was deallocated twice - once as the key
  and once in the zone node (the value). Fixed by adding parameters
  to ck_destroy_table() and ck_remove_item() which tells if the
  key and value should be deallocated (in case of value a pointer
  to destructor is passed).

Changes to other files to acommodate this change.