New module: XMonad.Prelude

This is a convenience module in order to have less import noise.  It
re-exports the following:

  a) Commonly used modules in full (Data.Foldable, Data.Applicative, and
     so on); though only those that play nicely with each other, so that
     XMonad.Prelude can be imported unqualified without any problems.
     This prevents things like `Prelude.(.)` and `Control.Category.(.)`
     fighting with each other.

  b) Helper functions that don't necessarily fit in any other module;
     e.g., the often used abbreviation `fi = fromIntegral`.

XMonad/Layout/BoringWindows.hs

@@ -36,8 +36,8 @@ import XMonad.Layout.LayoutModifier(ModifiedLayout(..),
                                     LayoutModifier(handleMessOrMaybeModifyIt, redoLayout))
 import XMonad(Typeable, LayoutClass, Message, X, fromMessage,
               broadcastMessage, sendMessage, windows, withFocused, Window)
-import Data.List((\\), union)
-import Data.Maybe(fromMaybe, listToMaybe, maybeToList)
+import XMonad.Prelude (fromMaybe, listToMaybe, maybeToList, union, (\\))
+import XMonad.Util.Stack (reverseS)
 import qualified Data.Map as M
 import qualified XMonad.StackSet as W