yaht now pure gfdl

Oops. I realised a couple of weeks ago that dual licensing Hal/GFDL on the PDF meant that I couldn't back-propagate wikibook patches into the LaTeX version. So now the PDF is GFDL only. Nice and simple.

(I dropped Hal an FYI and invited him to yell. Since it's _already_ GFDL anyway, I saw no reason that he would mind, which he does not seem to, cf no yelling)