workaround for co-existing green and non-green std{in,out,err}
workaround for co-existing green and non-green std{in,out,err}

applying O_NONBLOCK like io.files.File does will break behavior of
unpatched sys.std{in,out,err}, so a different fd-wrapping file object is
needed for just this use case.

the new _StdIOFile doesn't apply O_NONBLOCK, but always uses the poller
to wait for appropriate readiness before trying blocking reads/writes.

fixes #0000053

Change-Id: Idc0923d153a060b374775a79fa697d5d4e0afc70

teepark/greenhouse