It lives! The Cart lives! Shopping Cart Fixed
I’ve finally (as far as I know) got the cart working.
Please buy using the cart (and let me know of any problems with a comment here or an email).
Now I can get on with something more interesting. 
For anyone else trying to do this:
- Here are a good tutorial, the google tutorial for international shipping, the ISO country codes, google checkout sandbox docs, google shipping restrictions and address filters docs, and google geographic areas docs. It isn’t actually hard. Just fiddly, especially if you want to specify shipping for ‘Europe’.
- Use the sandbox until everything seems to be working. The sandbox gives better error messages.
- Use a binary chop (remove half of the code at a time) to identify the sources of errors. Start removing at the bottom so that your fields are always numbered contiguously from 1.
- Get your numbering exactly right. Many of my problems were a field number missed out or duplicated.
- Don’t try to include or exclude Andorra. Don’t mention Andorra.
- The Checkout may confuse Alabama and Albania, as regards shipping restrictions: Residents of Alabama will be able to choose shipping options for Albania. Don’t sweat it too much.
- Feel free to use my page source as an example.
- Test it with the live system. The live system is more stringent.