Baserock XML catalog files.

Includes base XML catalog DTDs and XHTML1 DTS and entity specificaitons.

The layout of the XML catalog files follows the debian layout described at:
http://debian-xml-sgml.alioth.debian.org/xml-policy/xml-catalogs.html

To install the initial catalog files:

make install

To link the catalog files to the root xml catalog:

./post-install.sh

xml-core/catalog.dtd retrieved from its canonical resource
http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd on 
12/3/14.

xhtml1-20020801/ retrieved from http://www.w3.org/TR/xhtml1/xhtml1.tgz
on 12/3/14.