Adding replicateM / replicateM_ to Control.Monad

[Simon Marlow]

> > The following is what I intend to commit. There's a gratuitious
> > foldM_ as well.
>=20
> You forgot to include the diffs for the documentation :-)

No he didn't, the diffs were empty since that module has no
documentation yet... 0.5 * :-)  (unless you count the library report,
but that's not subject to change, and it describes the Monad library
which is different from Control.Monad).

If anyone requires a diversion tactic from what they are currently
doing, spending an afternoon taking documentation from the Library
Report and Haddock-ising it into the sources in fptools/libraries/base
would be incredibly useful.  I made a start on the Prelude, but didn't
get very far.

Cheers,
	Simon