awful.util: change table.clone to do deep copies

Signed-off-by: Lukas Hrazky <lukkash@email.cz>
Signed-off-by: Julien Danjou <julien@danjou.info>

lib/awful/util.lua.in

@@ -339,8 +339,12 @@ end
 function table.clone(t)
     local c = { }
     for k, v in pairs(t) do
+        if type(v) == "table" then
+            c[k] = table.clone(v)
+        else
             c[k] = v
         end
+    end
     return c
 end