The second one should work..it doesn't? Are you looking it up at least in the context of a Session bean call? The sesson bean isn't a 2.1 session bean is it?
I added the code that does the lookup in your tutorial/entity/.../ShoppingCartBean. I tried those lookup names but all failed. Now I worked around this issue by passing the injected EntityManager around.
I also look forward to seeing a way to look up EntityManager in J2SE environment in the next preview.