Binary upgrade, fixes #85

This PR contains couple of features:

* Simple support for live binary upgrades
* Remove misleading connwatcher that does not work properly
* Track connections to sockets and emit stats 
I'm not sure I would understand this if I saw it in debug logs. How about something like:

    return fmt.Errorf("vulcand/server: failed to take file descriptor. I am running in TLS mode so I need a TCP listener, but the file descriptor I was given corresponded to a listener of type %T. More about me: %s. More about the bad file descriptor: %s", listener, s, f)