Putting this up for review not because you guys are interested in windows, but just because I'm hoping to do this with more of the decorators. Assuming nobody has any issues with this, I will do the rest without review.
expectedFailureWindows is equivalent to using the general expectedFailureAll decorator with oslist="windows". Additionally, by moving towards these common decorators we can solve the issue of having to support decorators that can be called with or without arguments. Once all decorators are always called with arguments, and this is enforced by design (because you can't specify the condition you're decorating for without passing an argument) the implementation of the decorators can become much simpler, which in turn will lead to less difficulties when moving from `unittest2` to `unittest` as well as supporting class level decorators for skip as well as xfail on all decorators.