The existing tests here didn't make much sense, and didn't cover all the
situations we care about. The 8 tests now check each of
client !--send-only EOF on stdin
client --send-only EOF on stdin
server !--send-only EOF on stdin
server --send-only EOF on stdin
client !--recv-only EOF on socket
client --recv-only EOF on socket
server !--recv-only EOF on socket
server --recv-only EOF on socket
The other thing we care about is whether the client/server keeps running
after the EOF. That is now checked in each of the tests too.