There is closefrom in some BSDs, but Linux ships this only as part
of libbsd. Add a new implementation of it in libreplace. The one in
libbsd of jessie and upstream differ and it has for example optimizations
for FreeBSD, but it gets some of the array calculations slightly wrong
from my point of view. If you want those, use libbsd. This replacement
is optimized on Linux only looking at /proc/self/fd/, everything else
would do the OPEN_MAX brute force fallback.
Signed-off-by: Volker Lendecke <vl@samba.org>