X.H.ManageHelpers: Factor doShiftTo out of transience and switch to W.shiftWin

Will be useful for shiftToLeader.

Use W.shiftWin instead of W.shift as it isn't guaranteed that the window
being managed by the ManageHook is still in focus.

XMonad/Hooks/ManageHelpers.hs

@@ -217,10 +217,7 @@ ledFrom = ask >>= liftX . withWindowSet . findTagLeader
 -- | A convenience 'MaybeManageHook' that will check to see if a window
 -- is transient, and then move it to its parent.
 transience :: MaybeManageHook
-transience = transientTo </=? Nothing -?>> move
-    where
-    move mw = maybe idHook (doF . move') mw
-    move' w s = maybe s (`W.shift` s) (W.findTag w s)
+transience = transientTo </=? Nothing -?>> maybe idHook doShiftTo
 
 -- | 'transience' set to a 'ManageHook'
 transience' :: ManageHook
@@ -239,6 +236,11 @@ shiftToLeader' = maybeToDefinite shiftToLeader
 maybeToDefinite :: (Monoid a, Functor m) => m (Maybe a) -> m a
 maybeToDefinite = fmap (fromMaybe mempty)
 
+-- | Move the window to the same workspace as another window.
+doShiftTo :: Window -> ManageHook
+doShiftTo target = doF . shiftTo =<< ask
+  where shiftTo w s = maybe s (\t -> W.shiftWin t w s) (W.findTag target s)
+
 -- | Floats the new window in the given rectangle.
 doRectFloat :: W.RationalRect  -- ^ The rectangle to float the window in. 0 to 1; x, y, w, h.
             -> ManageHook