Add support for Debian's GNU/kfreebsd

See http://sources.debian.net/src/cfengine3/3.2.4-2%2Bnmu1/debian/patches/626647-kfreebsd-support.patch for reference.
Merge branch 'master' of https://github.com/cfengine/core
Merge pull request #801 from bahamat/master

Add support for Debian's GNU/kfreebsd