additional tests + security issues

Hi Dan and others

You may be interested in

http://jena.sourceforge.net/test/grddl/

Three of these tests explore security issues.
I would like the jena implementation to refuse to honour the document() 
function at all, and disable some 'unsafe' XSLT2 features.

Unfortunately my code currently is failing those three security tests :(
I think that delays the first release.

I will be adding more tests as needed.

Jeremy