Fix misleading AttributeError tracebacks on Request objects.

[lovelydinosaur]

Closes #2108.

[foresmac]

Thanks for working on this. I ended up tracing the problem to an issue with my auth backend, but it took some doing to get there because the original stack trace was lost.

[lovelydinosaur]

@foresmac Most welcome - needed to be done.

[lovelydinosaur]

Some unrelated stuff in this commit - mostly due to a silent upgrade of pep8 (we might consider pinning it)

[foresmac]

FWIW, I'd feel better if these conditional and y or x lines were replaced with explicit Python conditional assignment statements.

return ('%s...' % x[:max(0, limit - 3)]) if limit and len(x) > limit else x

[lovelydinosaur]

Yeah. We're just cloning from the Django codebase here so I don't particularly mind that it's a bit rubbish in this case.