Additional header file

Christian Glahn sent me this patch to add a header file for a couple of
private functions of gdome2, gdome_xml_n_get_xmlNode, and 
gdome_xml_n_mkref.

Of course it is cleaner to not expose the private interfaces, however
this is necessary for XML::GDOME to be compatible with XML::LibXML.  This 
interface will not be documented, and I can add a warning to the header
file not to use these functions unless you know what you are doing.

XML::LibXML is one of the best and most widely used Perl XML modules.
With the XML::LibXML <-> XML::GDOME bridge, it will make XML::GDOME more 
useful because it can access the XSLT and SAX functions of XML::LibXML, 
and users of XML::LibXML can use the advanced DOM functions from 
XML::GDOME.  Hopefully this will lead to a greater collaboration and
better DOM functionality for all.

If there are no objections, I'll check this into CVS.

Thanks,
TJ