Moving basic functions

[Evan Laforge]

> 1. Add the infixl 4 operator "($>) = flip (<$)" to Data.Functor.
>
> 2. Move Control.Monad.void to Data.Functor, and reexport it from
> Control.Monad for compatibility.
> (Foreign.Marshal.Error.void is redundant, but should be kept as it is
> only marked as deprecated for half a year.)

One addition:

Foreign.Marshal.Error.void should also be a re-export.  This shouldn't
break anyone's code, but would mean that people typing 'import
Control.Monad; import Foreign' can use void without having to hide one
or the other.