[yocto] Any existing window manager that supports dual screens?

[Cui, Dexuan]

Hi all,
I'm booting Yocto Linux with some board that has 2 physical screens: one is traditional VGA output and the other is the on-board LCD screen.
I've managed to modify xorg.conf to make both screens work: i.e., I can move the mouse cursor on both two screens.

However, a screen shows the SATO desktop while the other shows nothing but a black screen -- surely when I move the mouse cursor on the screen, I can see the cursor.
I suppose this is because the default window manager (i.e., matchbox-wm) can't support dual screen? 

Could anybody point out if we have a more powerful window manager that has the support?
Does matchbox-wm-2 have the support?

BTW, I see there is a recipe gnome-session_2.30.2.bb in oe's side.
I think gnome-session should have the support? Maybe we can port it to poky?

Thanks!

-- Dexuan