While package comments shouldn't be novels, this throwaway word was not
sufficient (and wasn't mirrored in the `box` package).
This change attempts to include more reasoning without using too many
words.
Fixes golang/go#17673,golang/go#21139
Change-Id: I7fa11e2cd5b8e2010420cc14d784f9b0c65db6d2
Reviewed-on: https://go-review.googlesource.com/35910
Reviewed-by: Russ Cox <rsc@golang.org>
secretbox is supposed to append to the given slice, like hash.Sum() and
append(). However, I had a complete brain-fart: I've really no idea what
I was thinking of at the time.
R=golang-dev, sfrithjof, rsc
CC=agl, golang-dev
https://golang.org/cl/10099043