/** ALLWAYS call this method before including a class
    * by name from a request parameter, unless you use
	* this-> useClass or this-> tryUseClass
	* @param String $value the value to check
	* @return the value that was passed or trigger an error if not alphanumeric
	* 	_ and - are allowed because of formKey paths  
	*/
	function checkAlphaNumeric($value) {
		if ($value && preg_match("'[^A-Za-z0-9_\-]'", $value))
			throw new PntValidationException("Non alphanumerical characters in propertyname, type, handler or skinName: $value", E_USER_ERROR);
		else
			return $value;
	}