delay SSL socket wrapping

[Antoine Martin]

This would allow us to peek at the packet data and decide how to handle the client connection better, partially solving ticket:1213#comment:5.

We would then know if we're dealing with a browser / websocket request or with a plain SSL + TCP client connection.

The ssl=MODE option could then be used for bind-ssl sockets.

The difficulty with this is to ensure that we always eventually wrap the socket with an SSL layer if the user selected bind-ssl and not allow plain TCP / HTTP.