Do no treat GNU/kFreeBSD as a FreeBSD distro.

Related bug report: https://bugs.debian.org/739735

It seems FREEBSD affects `-ldl` flag and manpage directory, but in Debian GNU/kFreeBSD it should be in Debian fashion.
Merge pull request #487 from medicalwei/patch-1

Do no treat GNU/kFreeBSD as a FreeBSD distro.