fixes and a test demonstrating a problem with nullable relations

Hey,

As we discussed on twitter, I've been experimenting with the module.

First, MANIFEST contained a non-existing file, so it exploded.
Second, I added some resultset wrappers which was my original quest. Seems to be harmless.

But then I had an issue where writing into a NULLable relation didn't do anything, because it apparently hits the wrong code-path. I'm not entirely sure what's going on, so I've added a couple of tables, dbicdumped the new classes, and hopefully written a test-script that illustrates the issue.

Cheers,
Lars