divert-to has many advantages over rdr-to for proxies.  For example,
it is much easier to use, requires less code, does not depend on
/dev/pf, works in-band without the asynchronous lookup (DIOCNATLOOK
ioctl), saves us from additional port allocations by the rdr/NAT code,
and even avoids potential collisions and race conditions that could
theoretically happen with the lookup.
Heads up: users will have to update their spamd PF rules from rdr-to
to divert-to.  spamd now also listens to 127.0.0.1 instead of "any"
(0.0.0.0) by default which should be fine with most setups but has to
be considered for some special configurations.
Based on a diff is almost two years old but got delayed several times
... beck@: "now is the time to get it in" :)
Tested by many
With help from okan@
OK okan@ beck@ millert@