added some really ugly code to allow errors to propogate to

added some really ugly code to allow errors to propogate to
clients when writing to a rsync server

it works like this:

- we have an extra pipe from the receiver to the generator
- the server always runs with multiplexing on
- errors from the generator go down the multiplexed connection
- errors from the receiver go over the pipe, and from there to
  the multiplexed conn

it required some incredibly ugly code. damn.