fetch_assoc() fixes.

Signed-off-by: Norv <a.w.norv@gmail.com>
fetch_row() fixes and update of implementations in the Db classes.

Signed-off-by: Norv <a.w.norv@gmail.com>
free_result() fixes and update of implementation of db classes.

Signed-off-by: Norv <a.w.norv@gmail.com>
insert(), insert_id(), insert_sql() fixes and updates.

Signed-off-by: Norv <a.w.norv@gmail.com>