undo CL 12486043 / ab644299d124

Uglier.

??? original CL description
all: use strings.IndexByte instead of Index where possible

R=golang-dev, khr
CC=golang-dev
https://codereview.appspot.com/12486043
???

R=golang-dev
CC=golang-dev
https://codereview.appspot.com/12485044