Tag build swift-DEVELOPMENT-SNAPSHOT-2017-01-05-a
Merge remote-tracking branch 'origin/swift-3.1-branch' into stable

* origin/swift-3.1-branch:
  Follow-up for r289831: Lower the unjoined thread count to 100 in the libcxx-future.mm testcase.
  [tsan] Add interceptor for libcxx __shared_count::__release_shared()