libxml2 RELAX NG support

Daniel Veillard has being doing a lot of work on the RELAX NG support in 
libxml2.  The most recent release, 2.5.5, is quite conformant and seems 
to work for realistic RELAX NG schemas and documents. This is very good 
news because libxml2 is part of every modern Linux distro and gets 
installed on most modern Linux boxes.  In fact, since libxml2 doesn't 
yet have much W3C XML Schema support, I think we are now actually ahead 
of W3C XML Schema in terms of our support on the Linux platform.

You can validate a document against a RELAX NG schema using libxml2 just 
by doing:

  xmllint --noout --relaxng file.rng file.xml

If you're on a Linux box, I encourage you to try this out and report 
bugs (via bugzilla.gnome.org).  Daniel is very responsive to bug 
reports: everything I've reported in past releases has been fixed.

Congratulations and thanks to Daniel.

James