Replace AsRawFd implementations with generic AsInner<FileDesc>

[l0kod]

Revamp the AsRawFd implementations using generics.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @brson (or someone else) soon.

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[l0kod]

The same thing could be done for Windows extension as well. I can do it (without testing) if interested.

cc @aturon

[alexcrichton]

This unfortunately makes the implementors of AsRawFd impossible to find in the documentation itself because the AsInner trait does not show up in the documentation, and hence you're unable to find the total list of of all implementors.

[steveklabnik]

This doesn't merge cleanly anymore, and will ned a rebase.

[l0kod]

This unfortunately makes the implementors of AsRawFd impossible to find in the documentation itself because the AsInner trait does not show up in the documentation, and hence you're unable to find the total list of of all implementors.

Do I need to open an other issue for the documentation generation bug?

This doesn't merge cleanly anymore, and will ned a rebase.

Commit rebased.

[alexcrichton]

Oh I'm sorry I actually meant to close this earlier. Unfortunately the documentation issue is not actually a bug but rather is a feature. Private traits like AsInner shouldn't be showing up in the documentation.