I use Multisite almost exclusively and have been since version 3.1.3.
The lines:
define( ‘SITE_ID_CURRENT_SITE’, 1);
define( ‘BLOG_ID_CURRENT_SITE’, 1);
are there.
I fresh installed the site with 3.6 beta4 on June 26, 2013 and I now have 3.6.1.
I know how to install Multisite, thanks for asking.