I have a patch for the client side, but I don't find the option to attach a file to the ticket. So I posted it [http://www.tclcode.com/patches/tls-b5c41cdeb6-alpn.diff|here].

This patch adds an -alpn option that takes a list of protocols to offer in the Client Hello message. When the connection is established, the protocol selected by the server, if any, can be determined by checking the "alpn" key in the response of the tls::status command.