crypto/sha1: Make sha-1 do block mixup in place
crypto/sha1: Make sha-1 do block mixup in place

Benchmarks:

benchmark              old ns/op    new ns/op    delta
BenchmarkHash8Bytes          762          674  -11.55%
BenchmarkHash1K             8791         7375  -16.11%
BenchmarkHash8K            65094        54881  -15.69%

benchmark               old MB/s     new MB/s  speedup
BenchmarkHash8Bytes        10.50        11.86    1.13x
BenchmarkHash1K           116.48       138.84    1.19x
BenchmarkHash8K           125.85       149.27    1.19x

R=dave, rsc, iant
CC=golang-dev
http://codereview.appspot.com/6820096

Committer: Dave Cheney <bfcdf3e6ca6cef45543bfbb57509c92aec9a39fb@cheney.net>

pombredanne/go-deleteme,dsriram/golang,gnanderson/go,tv42/old-go,gnanderson/go,dsriram/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,apparentlymart/golang,dsriram/golang,apparentlymart/golang,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,dsriram/golang,gnanderson/go,apparentlymart/golang,dsriram/golang,apparentlymart/golang,dsriram/golang,pombredanne/go-deleteme,tv42/old-go,dsriram/golang,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,apparentlymart/golang,tv42/old-go,gnanderson/go