Misc. bugs in HsParser

[Simon Marlow]

> HsParser does not allow method declarations to follow a default
> implementation of a method.
> 
>     class G a where
>         f :: a -> a
>         f x = x
>         g :: a -> a
> 
> Optional semicolons or empty statements are not permitted in
> do-expressions.
> 
>     f x = do ;; x ;
> 
> That is probably the reason why this example fails to parse too:
> 
>     f x = do
>         y
>         where y = x

Thanks, both fixed.

Cheers,
	Simon