Doing expect_after before a child process has been spawned causes Expect
to try reading from stdin. If stdin is /dev/null, it gets an EOF from
the read, assumes it's been closed... and closes stdout too, so we don't
see any more of the child process interaction.
WIP because I've only done this for simh.
When shutting down the emulator and starting another, it's otherwise
possible for the first read from the new emulator to return an error
(EIO from the pty read in Expect).
WIP because I've only done this for simh...
