XMLConverter: fix errors in the DTD
XMLConverter: fix errors in the DTD

using "=" is a syntax error and the vertex position is optional: e.g.
separate buffers.
paroj/ogre,paroj/ogre,paroj/ogre,OGRECave/ogre,OGRECave/ogre,OGRECave/ogre,OGRECave/ogre,OGRECave/ogre,paroj/ogre,paroj/ogre