Bug 2617: matching raw-IPs against dstdomain

At present dstdomain handles a raw-IP hostname by performing rDNS and
testing against the domains list.

This causes major performance loss on systems with multiple dstdomain
ACLs. Since each one does its own rDNS lookup :(

I'd like some opinions please on how we can change this:

1) additional field in HttpRequest for the rDNS name. Set at first need.

2) change raw-IP hostname to rDNS when we get that info.

3) add rDNS as additional field to Checklist data, set at first need.

4) drop rDNS and match on raw-IP string directly.

Amos

-- 
Please be using
   Current Stable Squid 2.7.STABLE6 or 3.0.STABLE13
   Current Beta Squid 3.1.0.6