Expose the next event to the application

In improving JAXB performance, it helps to avoid unnecessary buffering.
Right now, when we unmarshal from XMLStreamReader, even though StAX API exposes
the parser-internal char buffer, JAXB still has to copy the characters into
JAXB's own buffer because the XML document might be:

  <foo>12<!-- comment -->34</foo>

When JAXB is looking at the CHARACTERS event, if we can know that the next token
is a start/end element. we can avoid copying the buffer. Looking at SJSXP source code,
I see that FragmentContentDriver actually has this information.

I wonder if SJSXP could expose this information as a proprietary extension to StAX,
so that we can take advantage of it in JAXB.
###@###.### 2005-05-11 17:31:43 GMT