[Yhc] Compiling Prelude.hs

[Neil Mitchell]

> code. Is it possible to remove the duplicated instances as well?
Yep, I removed them already - they were certainly a bug. It should be
in the repo already.

The compiler detects duplicate class declarations (good), but
supresses rename errors with the -redefine flag (bad, fixed now), and
doesn't detect duplicate instance declarations (bad, unfixed).

Thanks

Neil