Fix Broken SockFlag::SOCK_NONBLOCK and SockFlag::SOCK_CLOEXEC on MacOS/iOS#863

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kristate wants to merge 2 commits intonix-rust:masterfrom

kristate:sockflag_darwin_fix

Commits on Feb 22, 2018

nix::sys::socket: fix `SockFlag::SOCK_NONBLOCK` and `SockFlag::SOCK_CLOEXEC` on macos and ios; ref #244 #861
kristate
committed

Commits on Feb 23, 2018

nix::sys::socket: cover all cases of `struct SockFlag` and put a cfg gate on `test_sockflag_cloexec`; ref #244 #861
kristate
committed