Add flipped fmap

[Isaac Dupree]

On 04/08/10 13:10, Jonathan Cast wrote:
> The equational law relating<$>  to<*>  for Applicative instances is
>
>      f<$>  a = return f<*>  a
>
> We analogously have
>
>      a<$$>  f = a<**>  return f
>
> as well.  So the analogy between<$$>  and<**>  holds.

This parallelism also suggests to me that <$$> should be placed (only) 
in Control.Applicative, which is where <*>, <$>, and <**> reside.  Yeah, 
I know that's annoying...

-Isaac