message: include a message when the http server fails to start
diff: use config::{Config, Networks};
  use exe_common::sync;
  use handlers;
  -use iron::Iron;
  +use iron;
  use router::Router;
  use std::sync::Arc;
  @@ -11,13 +11,14 @@ pub fn start(cfg: Config) {
  start_http_server(cfg, networks);
  }
  -fn start_http_server(cfg: Config, networks: Arc<Networks>) {
  +fn start_http_server(cfg: &Config, networks: Arc<Networks>) -> iron::Listening {
  let mut router = Router::new();
  handlers::block::Handler::new(networks.clone()).route(&mut router);
  handlers::pack::Handler::new(networks.clone()).route(&mut router);
  handlers::epoch::Handler::new(networks.clone()).route(&mut router);
  info!("listenting to port {}", cfg.port);
  - Iron::new(router)
  + iron::Iron::new(router)
  .http(format!("0.0.0.0:{}", cfg.port))
  - .unwrap();
  + .expect("start http server")
  +}
  }
  