Proposal: Add missing Foldable/Traversable instances for Prelude types

[Ross Paterson]

On Fri, Jan 21, 2011 at 11:16:46PM -0500, Edward Kmett wrote:
> I went with the default being to avoid prematurely forcing a bottom when
> possible, to avoid being called out by the strictness police, but I'm not
> terribly wedded to the behavior.

There are two opposing police forces out there.  I'd prefer the strict
versions:

  foldMap f (e,a) = f a
  traverse f (e,a) = (,) e <$> f a

to match the fmap definition.