tags: put IM tag on the same screen as WWW tag

rc/tags.lua

@@ -40,6 +40,7 @@ shifty.config.tags = {
       position = 4,
       mwfact = 0.2,
       exclusive = true,
+      screen = math.max(screen.count(), 2),
       icon = tagicon("im"),
       nopopup = true,           -- don't give focus on creation
    }