fix broken compatibility for luajit 2.0.0

I recently start using moaigui to implement UI for my game. but my MOAI SDK is customized version which is integrated with luajit 2.0.0 and use it as script engine. so no more 'arg' variable for the function which accept argument as '...' so I patched moaigui to make it compatible for luajit 2.0.0. that's this pull request. except this problem, moaigui works perfectly well with my games. thanks for sharing your work. and it would be appreciated accept this PR for the user using luajit with MOAI SDK, like me.