#1 DTD errors

[Anders Thulin]

There seems to be a problem in problem.dtd: the
reprint element only accepts 'source' as children,
but pdbsamples.xml has 'text' in many, many places
(at least 600, if I can trust myerror reports).

Changing the definition of reprint to '(source | text)'
seems to work for this file, at least. As the
problem.dtd.doc mentions text when source is used for
reprint, I assume something like that is intended.

Furthermore, the entity 'neutral' has not been defined.
Adding an empty definition, similar to those for
black and white seems to be what's needed.