- Got rid of the checking of msg_fd_in in read_timeout() -- it was

  only needed back when the generator was reading a separate redo
  pipe from the message pipe.
- Fixed a potential data corruption in the data that the generator
  is sending:  if a message comes in from the receiver, we now make
  sure that we can't put the forwarding of this message to the sender
  into the middle of a multiplexed-write record that the generator
  is trying to flush.