Clean up stale mapped/waitingUnmap state in handle rather than unmanage.

This is an attempt to fix issue #96.  Thanks to jcreigh for the insights
necessary to fix the bug.

XMonad/Main.hs

@@ -143,7 +143,10 @@ handle (MapRequestEvent    {ev_window = w}) = withDisplay $ \dpy -> do
 
 -- window destroyed, unmanage it
 -- window gone,      unmanage it
-handle (DestroyWindowEvent {ev_window = w}) = whenX (isClient w) $ unmanage w
+handle (DestroyWindowEvent {ev_window = w}) = whenX (isClient w) $ do
+    unmanage w
+    modify (\s -> s { mapped       = S.delete w (mapped s)
+                    , waitingUnmap = M.delete w (waitingUnmap s)})
 
 -- We track expected unmap events in waitingUnmap.  We ignore this event unless
 -- it is synthetic or we are not expecting an unmap notification from a window.

XMonad/Operations.hs

@@ -77,7 +77,6 @@ unmanage :: Window -> X ()
 unmanage w = do
     windows (W.delete w)
     setWMState w withdrawnState
-    modify (\s -> s {mapped = S.delete w (mapped s), waitingUnmap = M.delete w (waitingUnmap s)})
 
 -- | Modify the size of the status gap at the top of the current screen
 -- Taking a function giving the current screen, and current geometry.