#206281 by keith.smith: document that people should look into the new system requirements when they upgrade

#175876 by hazexp, webernet, keith.smith: unify module/theme/translation download links and include more pointers to these locations

#152967 by keith.smith, webchick, Morbus Iff and KentByte: update the upgrade instructions for Drupal 6

#170638 by JirkaRybka and chx: move update access variable to settings.php, so we can check whether it is wide open, and we have one place for settings

   + reorganized ?q=admin/settings
   + deprecated the _settings hook

- Created separate upgrade instructions.  Will hopefully make it easier to spot upgrade isntructions.