SP6

[drewcrawford]

I am opening an issue for this. I have been working on it for awhile, but there is a LOT to fix. Self-assigning so somebody knows I have it.

I also have related tasks in atfoundation and atpkg.

[drewcrawford]

I have pushed swift-preview-6 branches to affected projects. They're not OK to merge, but if someone needs a working tree the tests pass.