Use lowercase indices when traversing ldap_get_entries result

As per http://www.php.net/manual/en/function.ldap-get-entries.php ldap_get_entries converts indices to lowercase in its return value, so the same was done in the getUserAttributes() function of GenericLDAPServer and ActiveDirectoryLDAPServer, when $fname/$sname/$mail_tag were being used as indices to the $data array returned by ldap_get_entries.