Code review comment for lp:~joke/bzr/bugfix353370

I agree with John about being careful when accessing sys.stdout
(even if StringIO objects provides a isatty()).

I'd also really like to have a comment there explaining the magic value
(why 10.000 and not 65536 or 1024 ?) and the intent (a value big enough
to never truncate lines ?).

I'll tweak and merge.