This validator returns FALSE if no rows are returned
by a given SQL query. If at least one row is returned
then the validator returns TRUE.
Rrequires the following custom attributes:
sql: query to find any related record. You may use field makers
that will be replaced by the corresponding request parameters passed
as a recordset to the isValid method.
(c) 2004 Martin Cordova
This code is released under the LGPL license
Dinamica Framework - http://www.martincordova.com
author: Martin Cordova (dinamica@martincordova.com)