Activate focused client with `awful.client.movetoscreen`

The default config has this:

    awful.key({ modkey, }, "o", awful.client.movetoscreen                        ),

This moves the client to the next screen and focuses that screen.

But it does not ensure that the client is raised above any existing
windows, e.g. when moving a floating client.

This patch emits the `request::activate` signal if the client is
currently focused, but only if the screen property actually has changed.

Closes https://github.com/awesomeWM/awesome/pull/98.

lib/awful/client.lua

@@ -542,8 +542,15 @@ function client.movetoscreen(c, s)
             s = sel.screen + 1
         end
         if s > sc then s = 1 elseif s < 1 then s = sc end
+        if sel.screen ~= s then
+            local sel_is_focused = sel == capi.client.focus
             sel.screen = s
             screen.focus(s)
+
+            if sel_is_focused then
+                sel:emit_signal("request::activate", "client.movetoscreen")
+            end
+        end
     end
 end