afuser: Fix compilation on FreeBSD

On FreeBSD, we need ->ut_name instead of ->ut_user, and the utmp stuff
needs an <inttypes.h> include. This patch adds those, and fixes #249.

Reported-by: Peter Czanik <czanik@balabit.hu>
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
control-server: Fix compile warnings

Do #include <string.h> in lib/control/control-server.c, because we're
using strlen() and similar functions defined therein.

Reported-by: Peter Czanik <czanik@balabit.hu>
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>