docker/docker — pull request #9248 by vbatts (2014-11-19 20:48:09+00:00)
Title: pkg/tarsum: actually init the TarSum struct

closes #9241
ping @jlhawn and @stevvooe

```
benchmark old ns/op new ns/op delta
Benchmark9kTar 45186 46167 +2.17%
Benchmark9kTarGzip 1081241 1024691 -5.23%
Benchmark1mbSingleFileTar 21924444 21059648 -3.94%
Benchmark1mbSingleFileTarGzip 62401725 62360958 -0.07%
Benchmark1kFilesTar 97972656 97298579 -0.69%
Benchmark1kFilesTarGzip 227488476 223579873 -1.72%

benchmark old MB/s new MB/s speedup
Benchmark9kTar 203.95 199.62 0.98x
Benchmark9kTarGzip 8.52 8.99 1.06x
Benchmark1mbSingleFileTar 47.83 49.79 1.04x
Benchmark1mbSingleFileTarGzip 16.80 16.81 1.00x
Benchmark1kFilesTar 10.70 10.78 1.01x
Benchmark1kFilesTarGzip 4.61 4.69 1.02x

benchmark old allocs new allocs delta
Benchmark9kTar 22 22 +0.00%
Benchmark9kTarGzip 74 74 +0.00%
Benchmark1mbSingleFileTar 345 345 +0.00%
Benchmark1mbSingleFileTarGzip 3368 3371 +0.09%
Benchmark1kFilesTar 71123 71124 +0.00%
Benchmark1kFilesTarGzip 141169 141392 +0.16%

benchmark old bytes new bytes delta
Benchmark9kTar 14201 14203 +0.01%
Benchmark9kTarGzip 1470322 1470322 +0.00%
Benchmark1mbSingleFileTar 41396 41363 -0.08%
Benchmark1mbSingleFileTarGzip 1906007 1906097 +0.00%
Benchmark1kFilesTar 2188442 2188440 -0.00%
Benchmark1kFilesTarGzip 10945384 10951599 +0.06%
```

Signed-off-by: Vincent Batts