Minor bug: listing display of the xml file is post-validation

[Klortho]

This is really a minor bug, and probably not worth addressing in the online validator. But when we produce a stand-alone validator, we should make sure it's not in it.

Right now, the listing of the XML file is from what comes out of the first pass through xmllint, which means that entities are all resolved, and other (mostly minor) differences from the original. So, the problem is that the listing doesn't match what was uploaded, and that might confuse users.

You can see this with internal-subset.xml: the copyright symbol is evaluated both in the internal subset itself, and in the body of the document. This could be fixed by passing the original XML to xpath-locator, which would mean that it, too, would have to read the DTD.