rpc: use httptest.Server for tests
rpc: use httptest.Server for tests

R=golang-dev, rsc1, rsc
CC=golang-dev
http://codereview.appspot.com/4253060

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

tav/go,tav/go,tav/go,tav/go,tav/go,tav/go,tav/go