Update masstree.
Update masstree.

The main reason is to fix a bug in 2fe20. This bug doesn't show
up under the flow allocator.

nathanielherman/silo,nathanielherman/silo,nathanielherman/silo,stephentu/silo,stephentu/silo,stephentu/silo,nathanielherman/silo,stephentu/silo