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/Main.hsc

@@ -98,7 +98,8 @@ xmonad initxmc = do
             , normalBorder  = nbc
             , focusedBorder = fbc
             , keyActions    = keys xmc xmc
-            , buttonActions = mouseBindings xmc xmc }
+            , buttonActions = mouseBindings xmc xmc
+            , mouseFocused  = False }
         st = XState
             { windowset     = initialWinset
             , mapped        = S.empty