vn_rdwr() no longer works the way it used to, giving invalid fd for vnode,
pipes and sockets. Undo the kernel work, make it back to vnode only, then
change userland to create tmp pipe /tmp/ and start an IO copy thread.
This brings us back to working send/recv with pipes, with Apple approved
kernel calls.
Ironically, userland starts a thread for dedup send/recv already.
Merge branch 'master' of github.com:zfs-osx/zfs