Conn should call shutdown on the inner stream when dropping

[sfackler]

This is pretty important for TLS connections so that they can perform the TLS connection shutdown messaging to allow for session reuse.

[sfackler]

@seanmonstar could you reopen? We still need to handle the client side.

[seanmonstar]

To clarify, is there a situation in the client where this doesn't happen? It look like in Dispatcher::poll, shutdown is called before returning Async::Ready(()) in all cases.

[sfackler]

Yep, looks like it is!