Proposal #2717: Add nubWith, nubOrd

[Bart Massey]

Ok, I've killed the overly ambitious proposal #2629, and replaced
it with the more modest proposal #2717
  http://hackage.haskell.org/trac/ghc/ticket/2717
which just adds Data.List.nubWith and Data.Set.nubOrd as previously
discussed ad nauseam.

I know at least one person thought that adding these was a bad idea, but some
others thought it was a fine thing to do.  Hence the discussion on this list.

    Bart Massey
    bart at cs.pdx.edu