Support pf rdr on Mac OS X 10.7, 10.8 and 10.9 by including the missing
Apple headers in the source tree and enable private Apple code. Since
we are using an interface marked private by Apple, this code is very
experimental.
Issue: #15
Reported by: Amit Chowdhary
OpenBSD 4.7+ and FreeBSD 9.0+ also include ipfw-style divert-to in pf,
so build ipfw NAT engine as well if pf is detected.
Reported by: Stuart Henderson
Get rid of the fragile glibc auto-detection mechanism and define
_GNU_SOURCE unconditionally in order to fix the build on recent GNU libc
systems such as Debian and Ubuntu. On non-GNU libc implementations,
_GNU_SOURCE should not have any effect.
Issue: #2
Reported by: Vincent Bernat