private void saveUndo() {
		markDirty(true);
		// RM_FP: undo files dont realy need to be in the data file path - but could be
		File f=new File(this.dataFilePath+"undo");
		
		if (!f.exists()) {f.mkdir();}
		if (undoOn) {
			undoIndex++;
			String nm=getUndoFile(undoIndex);
			if (undoVec.size()<undoIndex+1) {
				undoVec.add(nm);
			} else {
				undoVec.set(undoIndex,nm);
				while (undoVec.size()>undoIndex+1) {
					File delFile=new File(this.dataFilePath+undoVec.get(undoVec.size()-1));
					delFile.delete();
					undoVec.remove(undoVec.size()-1);
				}
			}
			fileUtil.save(nm);
			File delFile=new File(this.dataFilePath+nm);
			delFile.deleteOnExit();
		}
	}