[jdom-interest] support for parsers other than xerces

[Jason Hunter]

> I'm confused about which parsers JDOM supports.
> I can't find an answer in the FAQ or the list archives.

If you want to use SAX, any SAX 2.0 parser is fine.  If you want to use
DOM, any DOM Level 2 parser is fine.  We have adapters for most DOM
impls.  You can write your own adapter if there's one we don't have.

In the latest snapshot we support JAXP 1.1, so 'new SAXBuilder()' will
try to find a parser with JAXP first, but fall back to the Xerces
default if JAXP 1.1 isn't around.  I don't believe we should depend on
JAXP.

-jh-