There are some missing features, misspelled words and some technical bugs in the main db.php class. It's nothing big and has no effect on the security of the class and the original main functions of the class (except a certain few that you probably would rarely use).
One thing that I could point out right now that you would want to know about is the array set on line 31 ( var $sql_queries = array( ... ) )
It has a value that says 'SELECT DISCTICT'... it should be 'SELECT DISTINCT'. This would effect you if you try to use SELECT DISTINCT as a key to the array of the SQL you would pass into build_key_query() function. It would block SELECT DISTINCT and you won't be able to use that SQL command.
There are a few features I could add (and I will), but that is the main thing right now. I will re-upload the next db access wrapper class as soon as I get done.