wireproto: make a number of commands batchable Makes lookup, heads, known, branchmap, pushkey, and listkeys batchable. It could, for instance, be interesting to use this to batch calls to lookup when a pull or clone has multiple --rev arguments. The next patch is going to batch heads and known to slightly tune discovery.

wireproto: add batching support to wirerepository Adds the plumbing and wire call for batched execution, but does not batch-enable any methods yet.