/** Add a 'New' button if appropriate. If there is no idProperty, 
	* new objects can not appear in the list after they have been added, 
	* so a button for adding a new object will only confuse the user (inappropriate)
	* @param array $buttons Reference to the array to add the button to
	* @return boolean Wheather the new button was added
	*/
	function addNewButton(&$buttons) {
		$part = $this->getPropertyPart();
		$url = $part->getNewButtonUrl(); 
		if (!$url) return false;

		$buttons[]= $this->getButton("New",	"document.location.href='$url';");
		return true;
	}