C++ refactor proposal/warning for clustering.

[Alan Conway <ac...@redhat.com>]

I've written up some notes in doxygen format on some refactoring I need
to do for clustering. It also clears up some issues that irked my during
the 0-9 work. Would like to hear any opinions. 

I've attached HTML, generated from
cpp/src/qpid/cluster/doxygen_overview.h (I like the idea of writing
design proposals in doxygen, they may even end up as documentation!)

I'll be starting on this pretty immediately so speak up if you don't
like it. You have been warned :)

Cheers,
Alan.