This PR adds a "group hash", computed and maintained up to date as follows:
hash = 0
foreach member_id in group {
hash = xor(hash, member_id)
}It is a preliminary addition to enable services/processes to check whether they have the same view of a group, and could be used in a future ssg_group_refresh function to issue an RDMA operation only if the hash differs.
I'm marking this PR as a WIP; it should be rebased onto master once master gets updated with the branch that adds better error codes.