private static HashSet getAllAncestors(FlatNode node)
private static HashSet getAllAncestors(FlatNode node, boolean firstCall)
	private static HashSet getAllAncestors(FlatNode node) 	{	    HashSet ret = new HashSet();	    //add self	    ret.add(node);	    //add the upstream	    if (node == null || node.incoming == null ) 		return ret;		    for (int i = 0; i < node.incoming.length; i++)		RawBackend.addAll(ret, getAllAncestors(node.incoming[i]));	    return ret;	}