Lua: add optional additional init script, loaded at start up.

mod/box/box.lua

@@ -122,3 +122,8 @@ function box.on_reload_configuration()
         end
     end
 end
+local initfile = io.open("init.lua")
+if initfile ~= nil then
+    io.close(initfile)
+    dofile("init.lua")
+end