Fix for issue #687: handle AssertionErrors and AssumptionViolatedException by default again

Change the default behaviour of the `ExpectedException` rule back to handling `AssertionError`s and `AssumptionViolatedException`s by default, i.e. one does not have to call `ExpectedException#handleAssertionErrors()` or `ExpectedException#handleAssumptionViolatedExceptions()` to make the rule handle those exceptions.