Opt for replacements that avoid any assumptions
about the representations in use.

Passes toolstash -cmp.

Change-Id: Ia858a33abcae344e03fc1862fc9b0e192fde80c1
Reviewed-on: https://go-review.googlesource.com/20279
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>