CONTRIBUTORS: add Joseph Bonneau (Google CLA)

R=golang-dev, rsc
CC=golang-dev
https://codereview.appspot.com/7879044
crypto/cipher: fix vet warning

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/7973043
build: update assembly variable names for vet

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/7834046