go.tools/cmd/vet: enable test (fix build)
go.tools/cmd/vet: enable test (fix build)

R=r
TBR=r
CC=golang-dev
https://codereview.appspot.com/12482043

tmc/mirror-go.tools,t-yuki/go.tools.old,tmc/mirror-go.tools,t-yuki/go.tools.old,t-yuki/go.tools.old,tmc/mirror-go.tools