- merged sa_entity branch. the big change here is the attributes system

- merged sa_entity branch.  the big change here is the attributes system
deals primarily with the InstanceState and almost never with the instrumented object
directly.  This reduces lookups and complexity since we need the state for just about
everything, now its the one place for everything internally.
we also merged the new weak referencing identity map, which will go out in beta6 and
we'll see how that goes !