Followup to CL 129779 but also some other minor tweaks.

Change-Id: Id71455d8a14f5e33f82c942c9e892da56c49d17c
Reviewed-on: https://go-review.googlesource.com/c/149257
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>