remove a Set of keys from a Map

[Henning Thielemann]

I have (x :: Set key) and (m :: Map key a) and want to remove all keys and 
corresponding values from m that are in x. I could solve it efficiently 
with a

differenceSet :: Map key a -> Set key -> Map key a

or with a

Map.fromKeySet :: a -> Set key -> Map key a

or a

Map.fromKeySet :: (key -> a) -> Set key -> Map key a

but I did not find one of these functions in containers-0.4.2.