Make stable-2.6 compatible with newer pep8

This is done so that all current branches can run with newer pep8;
note that instead of fixing the problems (like I did on master), I've
just silenced more. These should *not* be merged onto master!

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>