- Moved the initialization of "itemizing", "maybe_PERMS_REPORT", and

- Moved the initialization of "itemizing", "maybe_PERMS_REPORT", and
  "code" from recv_generator() to generate_files() so that they
  don't get recomputed for every file (we pass them as args now).
- Allow protocols < 29 to call maybe_send_keepalive() so that we can
  try to flush the output buffer if things are slow (though we can't
  send a keep-alive packet without protocol_version >= 29).