Redirect replayed output to stdout/stderr by default

This patch flips the --redirect_output option on by default, and changes the runtime flag to --no_redirect_output.

The current behavior caught me by surprise.  I think it's possible in theory for redirecting to affect the integrity of the replay, but IMHO the slim odds of that arising are outweighed by the unexpectedness of the current behavior.  Or from another perspective, folks who are doing things that crazy should know how to disable redirecting.  Let me know if you disagree! :)