Fixed a nasty bug in unittest, where is we have a non-async test that throws an exception, followed…

Fixed a nasty bug in unittest, where is we have a non-async test that throws an exception, followed by an async test, the async test will not block and can end up 'passing' with no result set.

The problem is that when we throw the exception in the non-async test we don't break out of _nextBatch and we also add a call to _nextTestCase in _registerException. We should only do one of these; basically if the test is not async then we just stay in the _nextBatch loop; if it is async then we kick off the next test from in registerException.
Committed: https://code.google.com/p/dart/source/detail?r=12606

[Siggi Cherem (dart-lang), 2012-09-19 21:10:38]

lgtm