multiplexing over a single ssh connection

One of my friends at work today was complaining about darcs and the gazillion ssh connections it sometimes has to make, so I decided to take on zooko's feature request that we multiplex over a single ssh connection. It's not turning out to be very easy. One problem is that I need to work out how the business with launching the ssh control master is going to work. The thing has to be running in the background while darcs goes about it business. What I would like to be able to do is launch the thing, but wait until the connection has actually been established before returning. This way, the next time darcs wants to call ssh, it doesn't have to worry about the control master. Will have to think about this some more. In the worst case, we could just give friendly instructions on how to do this: I've already updated the FAQ on the wiki, suggesting that the user set DARCS_SSH='ssh -S the_control_file'.