docs: function MorayConnection(key, conn, hdl, log) {
      assert.string(key, 'key');
      assert.object(conn, 'conn');
      assert.object(hdl, 'hdl');
      assert.object(log, 'log');
      this.mc_key = key;      /* cueball identifier for this connection */
      this.mc_conn = conn;    /* object implementing Cueball "Connection" */
      this.mc_hdl = hdl;      /* cueball handle to release after drain */
      this.mc_log = log;      /* bunyan-style logger */
      this.mc_nreqs = 0;      /* number of outstanding requests */
      this.mc_state = MC_S_AVAIL;
  }