Example on linux_amd64 for 'go tool vet -h':

Before:
	Usage of /usr/local/go/pkg/tool/linux_amd64/vet:
After:
	Usage of vet:

Change-Id: I11cb16b656bd097062d57a8c7441fbe66caaef78
Reviewed-on: https://go-review.googlesource.com/29294Reviewed-by: Rob Pike <r@golang.org>