I think I broke CatalogResolver: what is it?

So, my tests started hanging. I debugged it and found the test code
was stuck waiting for an HTTP response from
http://www.w3.org/TR/xhtml-modularization/DTD/xhtml-blkstruct-1.mod
But this must mean CatalogResolver is no longer doing what we want
since it should use a local copy.

What is this code / where is it from? I found something similar in
Apache XML Commons but it's called Resolver. Is this an old version of
it, alternate version? I'm trying to get the source in order to track
down what's up.

Ruadhan I think you put in this magic originally?

Sean