This benchmark - in contrast to all other benchmarks - was
running the regexp match on 1-byte substrings of the input
instead of the entire input. Worse, it was doing so by preallocating
a slice of slices of every 1-byte substring. Needless to say,
this does not accurately reflect what happens when the regexp
matcher is given a large input.

Change-Id: Icd5b95f0e43f554a6b93164916745941366e03d6
Reviewed-on: https://go-review.googlesource.com/c/139778
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>