[xmonad] XMonad can't support _NET_ACTIVE_WINDOW" root window property.

Hi, develop team! I have use XMonad some month. It's great, thanks! But i found XMonad does not support the necessary root window property, namely "_NET_ACTIVE_WINDOW". Because i have a emacs extension for SCIM-Bridge need use this root window property to compute input focus position. And can use command "xprop -root _NET_ACTIVE_WINDOW" to test this problem, will got "_NET_ACTIVE_WINDOW: no such atom on any window." message. But in GNOME, this command will get value of "_NET_ACTIVE_WINDOW". So please add this root window property in XMonad. Thanks! -- Andy.