beautiful: set wallpaper of each screen

Signed-off-by: Julien Danjou <julien@danjou.info>

lib/awful.lua.in

@@ -824,10 +824,11 @@ end
 
 --- Spawn a program.
 -- @param cmd The command.
+-- @param screen The screen where to spawn window.
 -- @return The awesome.spawn return value.
-function spawn(cmd)
+function spawn(cmd, screen)
     if cmd and cmd ~= "" then
-        return capi.awesome.spawn(cmd .. "&", capi.mouse.screen)
+        return capi.awesome.spawn(cmd .. "&", screen or capi.mouse.screen)
     end
 end
 

lib/beautiful.lua.in

@@ -11,7 +11,11 @@ local print = print
 local setmetatable = setmetatable
 local awful = require("awful")
 local package = package
-local capi = { awesome = awesome }
+local capi =
+{
+    screen = screen,
+    awesome = awesome
+}
 
 local module_name = "beautiful"
 
@@ -64,7 +68,9 @@ function init(path)
             key, value = split_line(line)
             if key then
                 if key == "wallpaper_cmd" then
-                    awful.spawn(value)
+                    for s = 1, capi.screen.count() do
+                        awful.spawn(value, s)
+                    end
                 elseif key == "font" then
                     capi.awesome.font_set(value)
                 elseif key == "fg_normal" then