ZF-5957: Expose underlying Zend_Db_Select for Zend_Auth_Adapter_DbTable
Currently the underling DB Select object used for db-table auth is not exposed through a getter method.
$dbSelect = $this->_zendDb->select();
To $dbSelect = $this->getSelect();
and adding a getSelect public method.
Purpose: to add additional clauses/predicates to the authentication -- eg an enabled true/false.