Ability to re-run failed tests and list tests that have failed in editor-friendly form

[jeetsukumaran]

• re-run the last failed tests like nose does.
• list all the failed/error tests in the previous run in way that makes it easy to pass to an editor (perhaps a flag to switch between the dot-as-path form for the test runner and normal slashes + ".py" extension for the editor)

[Julian]

I have a similar comment here as in #38, which is that https://pypi.python.org/pypi/testrepository already exists and does this, so if you have #34, you'd be able to just use that, or for me, I'd be able to just keep using that