Do layout.arrange only once per main loop

This uses timer.delayed_call to arrange the layouts only once per main
loop.

lib/awful/layout/init.lua.in

@@ -16,6 +16,7 @@ local capi = {
     client = client
 }
 local client = require("awful.client")
+local timer = require("gears.timer")
 
 --- Layout module for awful
 -- awful.layout
@@ -96,6 +97,8 @@ end
 function layout.arrange(screen)
     if arrange_lock then return end
     arrange_lock = true
+
+    timer.delayed_call(function()
         local p = {}
         p.workarea = capi.screen[screen].workarea
         -- Handle padding
@@ -111,7 +114,9 @@ function layout.arrange(screen)
         p.screen = screen
         layout.get(screen).arrange(p)
         capi.screen[screen]:emit_signal("arrange")
+
         arrange_lock = false
+    end)
 end
 
 --- Get the current layout name.