Windows support

These are a few changes to better support Windows.  We may want to add a warning to the documentation that we don't really want to support Windows, but are just including it as is.
I'm fine with the change, @cpatrick can you give more explanation as to why this would break Heroku? I'm wondering if there is a solution that will work across all of the platforms in question.

(Paths with forward slash separators are nominally supported in the windows shell, but I guess not by the underlying system calls?)