kqueue(2) on macOS

The text ac5e4a11fb8f, as OS X 10.11.6, OS X 10.11.5, OS X 10.11.4, OS X 10.11.3, OS X 10.11.2, OS X 10.11.1, OS X 10.11 shipped it.

kernel event notification mechanism

kqueue(2) on macOS now