Updating /usr/src/sys to CURRENT

Hello list

Freebsd is not my main OS (yet), so I'm trying to update to CURRENT to try this
lists.freebsd.org/pipermail/freebsd-x11/2012-February/011445.html

So I put this in my ports-supfile and updated
*default release=cvs tag=.

Here it says
www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html
"Once you have synchronized your local source tree..."
OK, I synchronized the ports with csup, but now how do I synchronize
/usr/src/sys with CURRENT?
I still have the one that comes with 9-RELEASE.

Cheers
Ismael

-- 
Do not let me induce you to satisfy my curiosity, from an expectation,
that I shall gratify yours. What I may judge proper to conceal, does
not concern myself alone.