ParentPipe was a subset of EOFpipe, except EOFpipe correctly
accounts for theoretical(*) spurious wakeups on the pipe.
(*) AFAIK, spurious wakeups are/were more likely on TCP sockets
due to checksum failures, something that's not a problem on
local pipes. We're also not sharing pipes like we do with
listen sockets on accept(2), so there's no chance of another
process grabbing bytes (unless we have bugs in our code).