Make TwoPartyVatNetwork::onDrained() work correctly on the server side.  Previously only worked on the client side, where it's actually not very useful.  Fixes #71.  There's a deeper problem, though, that simply holding a capability received from the client will hold the dead connection open.
Regenerate bootstraps, which have been outdated for a while.
Cleaner disconnect handling.  Better fix for issue #71, and also simplifies the interface and improves robustness.
Merge branch 'master' of github.com:kentonv/capnproto