This increases the effectiveness of the
"integer-in-range" CL that follows.

Change-Id: I23b7b6809f0b2c25ed1d59dd2d5429c30f1db89c
Reviewed-on: https://go-review.googlesource.com/27651
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>