Re-add wallpapers to the themes

The commit "Remove all traces of awsetbg and wallpaper setters" removed these.
This commit adds them back, but they are now applied a little different. The
main reason is that this makes it really easy for the user to ignore the
wallpaper that a theme specifies.

Signed-off-by: Uli Schlachter <psychon@znc.in>

awesomerc.lua.in

@@ -1,4 +1,5 @@
 -- Standard awesome library
+local gears = require("gears")
 local awful = require("awful")
 awful.rules = require("awful.rules")
 require("awful.autofocus")
@@ -69,6 +70,14 @@ local layouts =
 }
 -- }}}
 
+-- {{{ Wallpaper
+if beautiful.wallpaper then
+    for s = 1, screen.count() do
+        gears.wallpaper.maximized(beautiful.wallpaper, s, true)
+    end
+end
+-- }}}
+
 -- {{{ Tags
 -- Define a tag table which hold all screen tags.
 tags = {}

themes/default/theme.lua.in

@@ -72,6 +72,8 @@ theme.titlebar_maximized_button_focus_inactive  = "@AWESOME_THEMES_PATH@/default
 theme.titlebar_maximized_button_normal_active = "@AWESOME_THEMES_PATH@/default/titlebar/maximized_normal_active.png"
 theme.titlebar_maximized_button_focus_active  = "@AWESOME_THEMES_PATH@/default/titlebar/maximized_focus_active.png"
 
+theme.wallpaper = "@AWESOME_THEMES_PATH@/default/background.png"
+
 -- You can use your own layout icons like this:
 theme.layout_fairh = "@AWESOME_THEMES_PATH@/default/layouts/fairhw.png"
 theme.layout_fairv = "@AWESOME_THEMES_PATH@/default/layouts/fairvw.png"

themes/sky/theme.lua.in

@@ -46,6 +46,7 @@ theme.taglist_squares_sel   = "@AWESOME_THEMES_PATH@/default/taglist/squarefw.pn
 theme.taglist_squares_unsel = "@AWESOME_THEMES_PATH@/default/taglist/squarew.png"
 
 -- MISC
+theme.wallpaper             = "@AWESOME_THEMES_PATH@/sky/sky-background.png"
 theme.taglist_squares       = "true"
 theme.titlebar_close_button = "true"
 theme.menu_height           = 15

themes/zenburn/theme.lua.in

@@ -8,6 +8,7 @@
 
 -- {{{ Main
 theme = {}
+theme.wallpaper = "@AWESOME_THEMES_PATH@/zenburn/zenburn-background.png"
 -- }}}
 
 -- {{{ Styles