Pre-Depends changed for dpkg on GNU/kFreeBSD

[Guillem Jover <guillem@debian.org>]

Hi!

In dpkg 1.17.13 I switched start-stop-daemon on GNU/kFreeBSD to use
the native kFreeBSD backend using libkvm instead of using the Linux
backend through linprocfs. Requiring linprocfs has always seemed
somewhat wrong to me, more so when on FreeBSD procfs is actually
optional.

This means the library is now part of dpkg's Pre-Depends only on
GNU/kFreeBSD. But I forgot to bring it up here as per policy §3.5
before the upload. Doing so now, but if there's no consensus, I'll
revert the change. Sorry about that.

Thanks,
Guillem