more path not working on windows

[Eh2406]

This is a follow up to #334. Are there other methods that require the same fix? rust-lang/cargo#5820 (comment) suggests that status_file() may need it? Are there others? rust-lang/cargo#5848 is waiting on getting this fixed, but I am not sure for witch methods?

How can we track down all of them, and make sure this doesn't come back?