Desugaring do-notation to Applicative

[Simon Marlow]

Following a couple of discussions at ICFP I've put together a proposal 
for desugaring do-notation to Applicative:

   http://ghc.haskell.org/trac/ghc/wiki/ApplicativeDo

I plan to implement this following the addition of Applicative as a 
superclass of Monad, which is due to take place shortly after the 7.8 
branch is cut.

Please discuss here, and I'll update the wiki page as necessary.

Cheers,
Simon