Prevent clean_html() method from splitting if /* is in attribute value

This is a dirty hack that prevents string such as this one from being split
when they, in fact, shouldn't:

  <xsl:sequence select="document($absoluteURI)/*/@external-id"/>

The /* in the XPath expression was interpreted as a JavaScript or CSS comment,
which caused this particular self-closing tag to be ignored when looking for
the previous open tag.
Rename all "lenght" variables to "length"