Motivation:
* Previously, the size of the compressed data was used for metrics,
rather than the uncompressed size. This causes the library to appear
to perform poorly relative to C or other implementation. Switch it
to use the uncompressed size so that it matches how decompression
benchmarks are usually done (like in compress/flate). This also makes
it easier to compare bzip2 rates to other algorithms since they measure
performance in this way.
* Also, reset the timer after doing initialization work.

Change-Id: I32112c2ee8e7391e658c9cf31039f70a689d9b9d
Reviewed-on: https://go-review.googlesource.com/17611Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>