add failing test case for prop-types Validating external propTypes

[arronmabrey]

@yannickcr this adds a failing test case for the following issue

https://github.com/yannickcr/eslint-plugin-react/issues/322

The first Foo case passes, and the second Bar case fails.

I'd be happy to help figure out a way to support this, I'm just not entirely sure how the linting processes works.

I also have a few other test cases in mind, but I figured I'd start with the simplest case first and see how that goes.