Data.Set whishes

[Simon Marlow]

> could the following be added to Data.Set?
>     * instance Ord element => Monoid (Set element)

Due to dependency issues, this would have to be defined in the Monoid
module, or later.

>     * subsetOf :: Ord element => Set element -> Set element -> Bool

This could be added (I agree with Ketil that isSubsetOf follows existing
conventions better).

Do you have a patch?

Cheers,
	Simon