Removed comment about renaming to archive_version_t.
Added cluster_version_t::LATEST_VERSION, ONLY_VERSION.
Moved around some assumption of local messages being serialized with the latest version.
Made send_message_write_callback_t::write take a cluster_version_t.
Made equivalent use of ONLY_VERSION in an applicable place.
Renamed connectivity_cluster_t::cluster_version to cluster_version_string.
Removed an RSI.
Made semilattice_manager_t<>::on_message actually use cluster_version.
Made directory_read_manager_t<>::on_message use the cluster_version.