Lusca: more reorganisation, new features

More Lusca updates!

I've further split up the client-side processing. Refresh, IMS handling, ETag handling, location rewriting and various range request support code is now in separate modules. The code isn't all that much easier to follow if you don't have a rough idea what is going on but it's getting there. One of the long-standing issues in the Squid/Lusca codebase is how much of the caching logic is done as part of the client-side handling; I'd like to continue slowly unwinding this so I can start sliding in processing hooks in useful places. I have eventual evil plans here; I'll talk more when they're coming closer to fruition.

I've also been whittling away a little at the lack of code documentation for the client-side request and reply framework. I'll commit some more comments to client_side.c and the associated routines as I explore things some more.

I've got a very overdue contract to sort out a TOS bit tagging feature. I'm putting in the basic framework to make this happen. The first step is a new ACL type - dstfwdip - which is the destination IP being handed the request. There's a bunch of other side-changes which need to occur before I can slot in the TOS marking map logic (and I still haven't figured out where -that- will be!) so stay tuned. The aim is to provide a simple way to tag client (and maybe also server) requests with TOS bits based on some property of the request - and this includes the destination IP/network the request is being forwarded to.