[GB.TEST.TAP]
* NEW: Assert.SubtestLevel is a new property that returns the number of nested subtests.
* NEW: Assert.BailOut always unwinds the subtest stack and bails out of the entire TAP session.
* BUG: Tests can bail out even if Finished was called.
[GB.TEST]
* NEW: Bail out again if errors from test methods are caught.
* BUG: Don't call Finish on a subtest when it was already finished.
After the Bail out message, we Quit with non-zero exit status to signal
an abnormal termination to the harness.
[GB.TEST.TAP]
* NEW: Add Reset() method to Assert. Useful if you use the same (automatic) instance for multiple TAP streams.
* BUG: Fix state handling in TapPrinter.Finished.
