We forgot to run typecheckrpc.go periodically and it didn't work
anymore and there were some minor errors in service/rpc2/client.go.
Rewrite typecheckrpc.go using go/packages, so that it works with go1.11
and go.mod, and fix the issues in client.go
Use godeps to vendor dependencies and the normal go toolchain, with
GO15VENDOREXPERIMENT=1 set to properly vendor dependencies for reproducible
builds.