Excludes don't appear to work on Windows

[thatch]

I don't yet understand why (not at a Windows machine), but I'm seeing CI failures that seem as if excludes passed to the TrailRunner.walk call don't work on Windows (they don't exclude files). Pathspec (at least the development version) contains code to normalize slashes, so I don't think that's it.

Here's the repro: https://github.com/thatch/hdeps/blob/1723b6bdb6a3752ce93b9e443b0fcaf5c6ba00c3/Makefile#L30-L31

Here's the api use in checkdeps: https://github.com/python-packaging/checkdeps/blob/743e1a6cc008065249cdc562843684bf0a1b99ff/checkdeps/cli.py#L121-L123

I will continue looking, just wanted to give a heads-up.