Found using the vet check in CL 106370045.

This is a second attempt at CL 101670044, which omitted the deps_test change.

This adds dependencies to net/rpc:

        encoding
        encoding/base64
        encoding/json
        html
        unicode/utf16

The obvious correctness and security warrants the additional dependencies.

LGTM=rsc
R=r, minux, rsc, adg
CC=golang-codereviews
https://golang.org/cl/110890043