Xfce 4.6 website update and release notes (tour)

[Jérôme Guelfucci]

> Awesome,could you also w3 validate the pages to iron out some browser problems.
Done, I fixed a bunch of issues, some are still remaining but I don't 
really know how to fix them.

Anyway, in the future we should update the website to remove tables 
which are missused in a lot of places and improve our CSS. But that's 
for later.

Jérôme