build: add tag date in changelog
Mac OS X support.

This includes bond, VLAN and bridge support. Mac OS X is pretty
similar to FreeBSD except for bonding which is different. Bonding code
is stolen from ifconfig.c. Header files from XNU are
shipped because they are missing from Mac OS X developer tools.

Still missing:
 - integration into launchd
 - homebrew formula
 - DMI part (through ioreg)
dmi: implementation for Mac OS X.

We use the IOKit framework.