kern/166780: [sysctl] [request] add sysctl for swap space used

[eadler at FreeBSD.org]

Synopsis: [sysctl] [request] add sysctl for swap space used

Responsible-Changed-From-To: eadler->freebsd-bugs
Responsible-Changed-By: eadler
Responsible-Changed-When: Thu Nov 8 20:54:41 UTC 2012
Responsible-Changed-Why: 
I won't be dealing with this PR for some time, so give it back to the
pool

http://www.freebsd.org/cgi/query-pr.cgi?pr=166780