CI and source pushback update

We have completed updating the CI machines to the latest beta release of Xcode 8. The Swift 2.3 and swift-3.0-preview-3-branch source pushbacks have also been completed. We hit an issue applying the associated diff for master, however, and have reverted it while we sort out the problem. We plan to apply a new diff tomorrow.

In the meantime, we are pushing changes to make master build with the new Xcode 8 beta release, and will re-enable CI shortly.