Errnos are available through multiple paths in nix

[Susurrus]

The current problem is the errnos (like EAGAIN) are exposed at nix::Errno::EAGAIN and nix::errno::EAGAIN. We should choose one "right" path and only expose these constants there. I'd probably keep Errno at nix::errno::Errno instead of re-exporting it in the root.

[jonas-schievink]

AFAIK reexporting enum variants is considered bad style (they're scoped for a reason)

[Susurrus]

Indeed. Would you be interested in taking this on and filing a PR to get this all cleaned up? I started working on this but the errno module needs more work than I realized.

[jonas-schievink]

I'm currently taking a look at #586, but after that's finished I can check this one out.