Reporters count correctly when :teardown fails/errors.

This is one more little tweak to the work you did on #49, which otherwise works very well.  Thank you.

When there is a failure or exception in a :teardown, ProgressReporter
was counting the test twice, resulting in a > 100% completion
percentage.

RubyMineReporter was counting the additional failure or error as a
separate test and logging a warning to the console.

* Add an :after_test callback to the reporters.
* Rename DefaultReporter's now-conflicting :after_test to
  :test_result.
* Both reporters report test completion status in after_test instead
  of in the various pass/fail/etc. methods.