Squashed 'vendor/src/github.com/tsenart/tb/' changes from 1fda845..f38b46e

f38b46e TestBucket_Take_Throughput: GOMAXPROCS(2)

git-subtree-dir: vendor/src/github.com/tsenart/tb
git-subtree-split: f38b46e5f10c4b08103ac6fdbe2318365d25b3cf
Update tsenart/tb

Merge commit '7ba2afcb6da2090fe8701e0ccdf52cef8fa65d32' into walker-split