Cacheboy: shuffling around the DNS code

I'm shuffling around the DNS code in preparation for some work toward an IPv6 core. Strictly speaking, I could have just left the dns code in src/ and IPv6'ed the raw network/socket layer but I've decided "basic" functional IPv6 support will require DNS support and so be it. It'll let me write test cases to make sure that the new code handles IPv4 and IPv6 DNS "right". I still don't know what "right" entails and I'm sure that journey will be very enlightening!

Its been more tedious than complicated. There's a bunch of config file parsing which needs to stay in src/ and I've split out the "libsqdns" DNS initialisation from the "squid" DNS initialisation. It compiles and runs here, resolving DNS requests happily, so I guess I'm mostly on track. I had to shuffle around some config variables so its entirely possible I've screwed that up somewhere.

This highlights the requirement for a much more sensible configuration management framework. It doesn't even have to be that complicated - just not the "one great big Config struct" that Squid currently has. I've got some plans in the back of my head to generic-ify that much later on down the track but it'll have to wait a while. It'll probably come in when the ACL code is split out into squid-specific and generic ACL types. (A lot of the ACL types aren't really specific to HTTP and in reality can be reused in a variety of network applications.)

So tomorrow I'll find some time to get the external DNS code working again which I hope will be slightly easier than the internal DNS code. Then I can let this codebase simmer for a bit, push Cacheboy-1.4 out the door and wait for it to stabilise before my next round of changes towards IPv6.