misc/emacs: add support for mode=count coverage

Use the same algorithm that go tool cover uses when producing HTML
output to render coverage intensity.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/12712043

Committer: Brad Fitzpatrick <bradfitz@golang.org>
net/http: Make ReadResponse work with a nil Request parameter

Fixes issue 5583

R=golang-dev, dave, bradfitz
CC=golang-dev
https://codereview.appspot.com/9821043

Committer: Brad Fitzpatrick <bradfitz@golang.org>