Changed FunctionTransform result type to node-set
* using xalan::FormatterToXercesDOM internally
** this required changes to the TransformationFacade::generate member method overloads
* TransformationFacade::generate now accepts references to xalan::FormatterListener instances
** "generate(std::basic_ostream<char>&..." instantiates a xalan::FormatterToXML and passes it to the actual generate member method
* changed ResultNodeFacade's "getNode" method into a "getResultElement" method
** xalan::FormatterToXercesDOM requires a xercesc::DOMElement instance instead of the previously available xercesc::DOMNode instance
** changed FunctionReadDirectory accordingly
* adapted FunctionTransform test case accordingly