Proposal #2769: Export mapAccumR from Data.Map, Data.IntMap

Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/2769 Discussion period: 1 week The `mapAccumR` function has been written in both the Data.Map and IntMap sources but it's commented out and not exported. This seems to be an error and I propose that it be simply uncommented. The issue can be worked around by using Data.List.mapAccumL on the descending list representation of the Map, but that's hardly optimal. Seems like a no-brainer to me, hence the short discussion period.