Remember if focus changes were caused by mouse actions or by key commands

If the user used the mouse to change window focus (moving into or clicking on a
window), this should be handled differently than focus changes due to keyboard
commands. Specifically, it's inappropriate to discard window enter/leave events
while the mouse is moving. This fixes the bug where a fast mouse motion across
multiple windows resulted in the wrong window keeping focus.

It's also helpful information for contrib modules such as UpdatePointer - it's
supposed to move the mouse pointer only in response to keyboard actions, not if
the user was moving the mouse.

XMonad/Core.hs

@@ -69,6 +69,7 @@ data XConf = XConf
                                       -- ^ a mapping of key presses to actions
     , buttonActions :: !(M.Map (KeyMask, Button) (Window -> X ()))
                                       -- ^ a mapping of button presses to actions
+    , mouseFocused :: !Bool           -- ^ was refocus caused by mouse action?
     }
 
 -- todo, better name