Fix all flake complaints in crumbs.

We can now (next commit) test flake8 output as well as tests.
Add travis checks of flake8 output.
Add definition of ResourceWarning if not present.

Seems that python2 doesn't include ResourceWarning whereas python3 does.
In order to make the code a touch more portable, we're adding that
definition.

Also, this would have been caught if we had already been using travis's
fast fail option to stop as soon as we get a failure.  The flake8 error
indicating this problem would have been more prominent.

I'm getting some weird test output from nose when I run with python2 but
hoping that travis can tell me if it's actually a concern or not.
Add builtins check for ResourceWarning.

Another python2 vs python3 item meets the dust.  Seems that __builtin__
changed names from 2 to 3 and we need to use that in conjunction with
the check for ResourceWarning to properly support both languages.

Also added in this commit is a more robust treatment of preparation in
the travis configuration.