leaking file descriptors

[hannesm]

in unix/lwt/lwt-tls, the code snippets:

    let sock = Unix.(socket sd st 0) in ...
    try
      Unix.connect sock sa ;
      s := Connected sock;
      Ok ()
    with
    | Unix.Unix_error (e, f, _) -> ... Error err

are suspicious -- when connect fails, the sock has been allocated (by socket) but is never closed (only called at_exit and when send fails).