Fixed JSendMixin hanging up if auto_finish was disabled

If you somehow disable self._auto_finish, JSendMixin hangs the whole thing up because (I think) it relies on auto_finish to finish imidietly after write(), and you disable that, it hangs right after write.
So I fixed it by appending self.finish() after every write in every JSendMixin method. If auto_finish = true, it does nothing, if it's false, it finishes properly.
In my case, I had to disable auto_finish using decorator to implement asynchronous @auth.