* os::pipe() now returns IoResult<os::Pipe>
* os::pipe() is now unsafe because it does not arrange for deallocation of file
descriptors
* os::Pipe fields are renamed from input to reader and out to write.
* PipeStream::pair() has been added. This is a safe method to get a pair of
pipes.
* Dealing with pipes in native process bindings have been improved to be more
robust in the face of failure and intermittent errors. This converts a few
fail!() situations to Err situations.
Closes#9458
cc #13538Closes#14724
[breaking-change]