Cluster: keys slot computation now supports hash tags.

Currently this is marginally useful, only to make sure two keys are in
the same hash slot when the cluster is stable (no rehashing in
progress).

In the future it is possible that support will be added to run
mutli-keys operations with keys in the same hash slot.
Don't count time to feed MONITORs in SLOWLOG.
Cluster: redis-trib: options table entry for add-node fixed.
Old Changelog file removed from unstable branch.
Added a release notes file good for "unstable".
Cluster: added signature + version in bus packets.
Cluster: discard bus messages with version != 0.
Cluster: signature changed to "RCmb" (Redis Cluster message bus).

Sounds better after all.
Cluster: don't propagate PUBLISH two times.

PUBLISH both published messages via Cluster bus and replication when
cluster was enabled, resulting in duplicated message in the slave.
Cluster: clusterReadHandler() fixed to work with new message header.
Cluster: redis-trib del-node variable typo fixed.
Cluster: replica migration should only work for masters serving slots.
Cluster: clear the FAIL status for masters without slots.

Masters without slots don't participate to the cluster but just do
redirections, no need to take them in FAIL state if they are back
reachable.
Cluster: fixed inverted arguments in logging function call.
Cluster: redis-trib, more info about open slots error.
Cluster: update configEpoch after manually messing with slots.
Cluster: ignore slot config changes if we are importing it.
Cluster: don't update slave's master if we don't know it.

There is no way we can update the slave's node->slaveof pointer if we
don't know the master (no node with such an ID in our tables).
redis-trib: log event after we have reference to 'master'.
Cluster: redis-trib fix: cover new case of open slot.

The case is the trivial one a single node claiming the slot as
migrating, without nodes claiming it as importing.