Updated OWIN to the latest ServiceStack

First I fast-forwarded master (no pull request for that, you can do that easily on your own) and then merged the latest SS master into OWIN-1.0.

Had to add a few more IHttpRequest property implementations, and updated the unit test project to use newer NuGet packages for the hosting libraries.

I wasn't able to get the test that runs the self host to work, I'll continue to look at it but didn't think it should hold up getting this PR in.