Some more tests from Clint Ruoho. The main branch of Instiki (and, I guess,
the old sanitizer) are vulnerable.
Also: under Ruby 1.8.x, CGI.unescapeHTML screws up horribly decoding NCRs
which represent high-bit ASCII characters. UTF-8 agrees with 7-bit ASCII,
but CGI.unescapeHTML doesn't seem to know that they disagree for i>127.
Fixed a bug in the HTML5lib tokenizer (affects S5 slideshows).
Some miscellaneous code cleanup. In particular, don't bother with zapping control characters;
instead, rely on is_utf8? method to raise an exception (which we do anyway).
