builder: label the race builder as "race"
builder: label the race builder as "race"

R=golang-dev, adg, dave, rsc, minux.ma, dvyukov
CC=golang-dev
http://codereview.appspot.com/6648043

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang