support for FreeBSD

A very simple update to support FreeBSD.  Note that MacOS X's userland is basically pulled directly from FreeBSD (for example, on your Mac, run `strings /bin/ps | grep FreeBSD`), so I've changed the Mac provider to be named BSD and have both FreeBSD and Macs point at that.  I suspect that an equivalent change would also support NetBSD and OpenBSD, but I don't have either of them handy to test with.