XMLStreamReaderHandle offers no way to close the underlying InputStream

I just discovered that XMLStreamReader.close() does not close the underlying input source.  That means we need a way clients can tell us to close the InputStream we hand to XMLStreamReader.receiveContent().  We will add a close() method to XMLStreamReaderHandle which explicitly will close the input source.

This affects b3_0, b2_0, and b1_0.
