add pipe2 to non-OSX BSD's

[oconnor663]

#500

[rust-highfive]

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

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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[alexcrichton]

@bors: r+

Thanks!

[bors]

📌 Commit 7c06730 has been approved by alexcrichton

[bors]

⌛ Testing commit 7c06730 with merge bce927b...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing bce927b to master...