Fix missing screen refresh when new posts arrive.

Fix missing screen refresh when new posts arrive.

The rework of resize handling had the accidental side effect that when
the self-pipe from the stream-watching thread signals us, we do call
extend_future() on our feeds, but we _don't_ loop back round to the
screen redraw, so that if the user is sitting in their home timeline,
the bottom line of the screen doesn't update to show that new stuff is
available.