[libxml++] Validation implemented

[Murray Cumming <murrayc usa net>]

I just added validation to the parsers. It should be a simple matter of
calling Parser::set_validation(), as you can see in examples/dom_parser/.
Please test. I plan to release a new tarball with this at the weekend.

I have non-valid and valid examples in that directory, but I would like better
examples - the problem is that I always forget the syntax for DTDs.


Murray Cumming
murrayc usa net
www.murrayc.com