Extract information from more kinds of wedged directory connections.

In main.c, we do:

    /* This check is temporary; it's to let us know whether we should consider
     * parsing partial serverdesc responses. */
    if (conn->purpose == DIR_PURPOSE_FETCH_SERVERDESC &&
        connection_get_inbuf_len(conn) >= 1024) {
      log_info(LD_DIR,"Trying to extract information from wedged server desc "
               "download.");
      connection_dir_reached_eof(TO_DIR_CONN(conn));

We should also, at a minimum, do this for microdesc downloads.