Remove an invalid attribute in longindex.html
For some reason, the stylesheets generate a
<div xmlns:xlink="http://www.w3.org/1999/xlink" ...> element in
longindex.html, but this is not valid in xhtml (the attribute
xmlns=xlink is not defined in the DTD). The problem is that tidy then
thinks it is not a true xhtml and removes the doctype declaration.
But when a browser receives a file without doctype declaration, it
thinks it uses an old standard, and switches to "quirks mode"
(for firefox, this can be seen by typing ctrl-I on the page).
