spawn() and readandwrite() are documented as being variants of run() which
do not block the command line. yet in an @async, run() seems to yield to
other tasks. to wit:
# bar prints first because it's the first task
julia> @sync begin
@async println("bar")
@async (run(`sleep 10`);println("foo"))
end
bar
foo
Task (done) @0x00007f87c088fba0
# but why does bar print first here?
julia> @sync begin
@async (run(`sleep 10`);println("foo"))
@async println("bar")
end
bar
foo
Task (done) @0x00007f87c08b3f60
note that the behavior is the same if i replace the `sleep 10` with a
`touch foo`.
