Merging sockaddr_rework into Cacheboy trunk

I'm slowly cherrypicking bits and pieces of the Cacheboy sockaddr_rework into trunk. I've merged in the no_addr/any_addr tidyup which makes those comparisons and sets much clearer. I'll next bring over the sqinet_ routines as just files, ignoring the change history. I'll then bring over the changesets implementing the sqinet_ changes to the comm code and main codebase, retaining the basic change history.

I now need some live testing under decent amounts of real traffic so I can make sure I haven't missed some silly corner condition in the base comm code.

All of this work exposed some of the ugliness that happens in the IPC code with filedescriptor creation that bypasses the comm layer. Basically, the IPC helper code creates file descriptors itself and uses fd_open() to tell Squid about them but then unconditionally uses comm_close() to close them. This is .. stupid.

I may drop in some debugging code to ensure that only sockets created by the comm layer are closed by comm_close(). I wonder how many bad uses of file descriptors will be caught out by that..