Add PEER.exists to make it easier to check for the validity of a name
Lift out much of the resolver logic into a structure more suitable for Vchan

Specifically, vchan doesnt have a listen call as sockets do, so we need
to move to a Conduit-based solution for that.  Resolvers now register
vchan uuids to publish them in the namespace upon startup
Merge branch 'master' of github.com:avsm/ocaml-conduit
More fixes of the APIs to better support both forms of vchan