/** If the class does not exist, try to include it 
	 * @param string $className name of the class
	 * @param $dir application folder path
	 * For each class name inclusion is first tried from $thisfunction tryUseClass(->getDir(), 
	 * 	    If the class is not found, a class from the classes root folder is tried.
	 *      However, this behavior may be overridden on Site::getTryUseClassTryParams
	 * @return boolean wheather a class file was included. Also true if the class already existed.
	 */
	function tryUseClass($className, $dir) {
        if (strlen($className) > Gen::$CLASS_MAX_LENGTH)
            throw new PntValidationException("$this - class name too long: '$className'");

		$this->checkAlphaNumeric($className);
		pntCheckIncludePath($dir);
		$params = $this->getTryUseClassTryParams($className, $dir);
		$included = Gen::tryIncludeClass($params[0][0], $params[0][1]); //tryUseClass
//print "<BR>tryIncludeClass(".$params[0][0].", ". $params[0][1].") $included";
		if (!$included) {
			$included = Gen::tryIncludeClass($params[1][0], $params[1][1]); //tryUseClass
//print "<BR>tryIncludeClass(".$params[1][0].", ". $params[1][1].") $included";
		}
		return $included;
	}