[testlib] fix page validator selection. Closes #2869456 * use a validator that checks XML well-formness for the html5 doctype (as a convenient side-effect, it does not choke on e.g. a canvas tag like the HTMLParser does) * use a DTD validator if there is an xml declaration * else use the HTMLValidator

\.svn
^build$
^dist$
\.pyc$
\.pyo$
\.bak$
\.old$
\~$
\#.*?\#$
\.swp$
^doc/book/en/apidoc$
\.old$
syntax: regexp
.*/data/database/.*\.sqlite
.*/data/database/.*\.config
.*/data/database/tmpdb.*
.*/data/ldapdb/.*
^doc/html/
^doc/doctrees/
^doc/book/en/devweb/js_api/