Xml2 on Windows

<<xml2.patch>> The attached patch fixes the xml2 contrib module for
windows, by changing the order of -lxslt & -lxml2 (yes, after 2 releases
that's all it took!). Tested on Windows & Linux.

It might be worth manually testing this on any other platforms that
might be sensitive to the library order - this module is *not* tested by
the buildfarm (perhaps an autoconf change would be appropriate to build
it if libxml/libxslt are on the build machine, but that's a whole other
problem)

This completes todo item "Port contrib/xml2".

Regards, dave.