Only the pointer to the data is stored in the hash table,
no space is malloced for the data!
Parameters:
h - Hash table to insert to
key - Key to insert
keylen - Length of that key
dataptr - Dataptr to insert
Returns:
int ret == 0: OK.
int ret == -1: An error, see pbl_errno:
PBL_ERROR_EXISTS - An item with the same key already exists.
PBL_ERROR_OUT_OF_MEMORY - Out of memory.