Possibly ancient history non-compliance.

[Simon Marlow]

> ghc-4.04 and ghc-4.08 both complain about the following:
> 
>     No instance for `Show HandlePosn'
> 
> But according to the report, they should be showable (if precious
> little else).

Yes, it does appear to be missing, and it's still missing in 5.02.  I'll
try to get around to fixing it before the release.

Cheers,
	Simon