Implement _NET_DESKTOP_NAMES, this one was a bit tricky since thespec

says that a pager can change the property at any time (most need a
clientmessage). So deal with property updates.

Needed to shuffle some of the other code around since we can't just use
shortcut_to_name[] everywhere now.

ok okan@

xutil.c

@@ -189,6 +189,7 @@ char 		*atoms[CWM_NO_ATOMS] = {
 	"_NET_DESKTOP_GEOMETRY",
 	"_NET_VIRTUAL_ROOTS",
 	"_NET_SHOWING_DESKTOP",
+	"_NET_DESKTOP_NAMES",
 };
 
 void