Fixed stash usage in ck_rehash() and ck_insert_item():
  - cannot copy the pointer because the array may be reallocated
  - TODO: maybe use also rcu_dereference().
Changed way of working with dynamic array:
  - function da_reserve() only makes sure there is enough place in
    the array; added function da_occupy() to really increment the
    item count
  - fixed ck functions to use the array properly.
Bugfix in ck_rehash():
  - was not resizing the stash properly.
Bugfixes in ck_dump_table():
  - wrong accessing of items
Bugfix in da_resize():
  - was not copying the array contents!