* html files are now stored as follows:
If the html file is valid xml, store as html/stuff.xml
If it's not, store as html/stuff.xml, which contains
<html meta1="..." filename="stuff.html">,
and html/stuff.html, which actually contains the contents.
Warn if the contents are not parseable with lxml's html parser,
but don't error.
* for parseable html, strip out the html tag when storing, so that it isn't
rendered into the middle of a page
* lots of backcompat to deal with paths. Can go away soon.
* fix output ordering in clean_xml
