With most recent Roslyn preview

Not sure you want to pull into master branch though. There is one skipped test, one failed test. The fail is simple, we didn't add enough reference dlls to the compilation, but I'm not sure how it worked in the old version of Roslyn. Can review later.
Any idea if this is going to come back at some point, if it was changed to a different error, or simply obsoleted? We can remove this test if that this error code no longer applies