Implement _NET_VIRTUAL_ROOTS (just clear it, we don't use that technique)

and _NET_SHOWING_DESKTOP (we're never doing so right now).

only three informational root-window hints to go.

ok okan@

xutil.c

@@ -187,6 +187,8 @@ char 		*atoms[CWM_NO_ATOMS] = {
 	"_NET_CURRENT_DESKTOP",
 	"_NET_DESKTOP_VIEWPORT",
 	"_NET_DESKTOP_GEOMETRY",
+	"_NET_VIRTUAL_ROOTS",
+	"_NET_SHOWING_DESKTOP",
 };
 
 void