* add native_fflush libc passthru
* add `pipe2` which combines `pipe` and `fcntl` - see docs
* POSIX subprocess: incorporate async reader capability and and fflush for writer
* use the real-name O_NONBLOCK since it's available
* typo
* ok... remove `pipe2` and do this with an existing method......
* Update releasenotes.md
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Co-authored-by: Christoffer Lerno <christoffer@aegik.com>