Iterator movement function.

Move this iterator to the specified key k, by default moves exactly to k, and update cached data element, you can also specify DB_SET_RANGE, to move to the biggest key smaller than k. The btree/hash key comparison routine determines which key is bigger. When the iterator is on a multiple container, move_to will move itself to the first key/data pair of the identical keys.

0 if succeed; non-0 otherwise, and this iterator becomes invalid. Call db_strerror with the return value to get the error message.