On making a brand new installation of '2.4beta (Build: 20121109)' under LAMP I've made a mistake using a wrong DB name => found the missing:

public function create_database($dbhost, $dbuser, $dbpass, $dbname, array $dboptions=null) {

...

        if (!$result) {

            throw new dml_exception('cannotcreatedb');

        }

...

Time to enhance the codechecker to look at the string being declared vs being requested?