pep8 does not fail #250

[tnelling]

I'm not sure why - my local testing suggested that any pep8 failure would be detected, but #250 has the wrong tab size, yet it doesn't fail 0.12-block-pep8.py.

I had intended to add #250 as a test case for a new unit test in 0.25-block-test-failures.py. I'll still do that when I have the chance.