* qemud/qemud.c, qemud/bridge.c, qemud/iptables.c: fix
our FD_CLOEXEC usage so that all fds which should be
closed on exec are marked as such and that we leave
exec() to do the actual closing.
* qemud/iptables.[ch]: add code for managing iptables
rules.
* qemud/Makefile.am: add iptables.[ch].
* qemud/qemud.c: add and remove iptables rules as
appropriate.
* qemud/conf.c: when starting a guess, add a rule
allowing it to forward packets across the networks
bridge.
* qemud/internal.h: add iptables context ptr
* configure.in: add --with-iptables-dir and
--with-iptables-prefix to allow us to put our rules
in a chain with the given prefix and save the rules
in files in the given dir so as to integrate with
the proposed "service iptables restart" solution
in:
https://bugzilla.redhat.com/227011
