Re-set wallpaper on screen's property::geometry

Imagine that you have two screens of different resolution and you change their
position (xrandr --output first --left-of second). Of course, the wallpaper has
to be updated afterwards.

This commit makes the default config do that.

Fixes: https://github.com/awesomeWM/awesome/issues/1102
Signed-off-by: Uli Schlachter <psychon@znc.in>

awesomerc.lua

@@ -165,8 +165,7 @@ mytasklist.buttons = awful.util.table.join(
                                               awful.client.focus.byidx(-1)
                                           end))
 
-awful.screen.connect_for_each_screen(function(s)
-    -- Wallpaper
+local function set_wallpaper(s)
     if beautiful.wallpaper then
         local wallpaper = beautiful.wallpaper
         -- If wallpaper is a function, call it with the screen
@@ -175,6 +174,14 @@ awful.screen.connect_for_each_screen(function(s)
         end
         gears.wallpaper.maximized(wallpaper, s, true)
     end
+end
+
+-- Re-set wallpaper when a screen's geometry changes (e.g. different resolution)
+screen.connect_signal("property::geometry", set_wallpaper)
+
+awful.screen.connect_for_each_screen(function(s)
+    -- Wallpaper
+    set_wallpaper(s)
 
     -- Each screen has its own tag table.
     awful.tag({ "1", "2", "3", "4", "5", "6", "7", "8", "9" }, s, awful.layout.layouts[1])