http server: don't send trailing '0' for chunked encoding when responding with 304 NotModified
http server: don't send trailing '0' for chunked encoding when responding with 304 NotModified

R=rsc, adg
CC=golang-dev
http://codereview.appspot.com/2723041

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go