Expand #content on non-admin pages

Nice theme!

If there is only one sidebar (or no sidebars) on the page, then the center #content div should expand wider.

This patch handles the cases when there is only 1 sidebar. I haven't added a css class for "no-sidebars", however this should be really easy based on what's here.

Note that this $body_classes variable that's being build in this patch is part of the PHPTemplate engine in Drupal 6, so you should be able to just add the same code into the page.tpl.php and styles.css file for the D6 version of Burnt and you shouldn't need to change template.php at all.