New FEC framework, with unit tests.

For review. This works, but it's not to be merged just yet because nothing uses it yet. The new post-db4o client layer will use it heavily.
Good point ... except that FECJob *is* a database class, so it would be rather confusing. FECQueue uses the database, but could be renamed. FECCallback is an interface implemented by database objects, I'm not sure whether we could rename it easily.