Make the public html pages valid xhtml, and validate more RDFa cases.

Also after I spent time playing with the w3c online validator,
I decided it was best to try and add modest validation to my
unit tests.

So now there's a validate_xhtml function in ethelp.

The one really weird thing is I tried to load the DTD
in the test case, however it looks like librdf clobbered the
XML catalog resolver at some point so the DTD resolver can't
find anything.