Cluster: redis-trib set-timeout implemented.
Don't log MONITOR clients as disconnecting slaves.
Fixed inverted if condition in MISCONF error code path.
Cluster: introduced repl_offset fields in clusterNode.

The two fields are used in order to remember the latest known
replication offset and the time we received it from other slave nodes.

This will be used by slaves in order to start the election procedure
with a delay that is proportional to the rank of the slave among the
other slaves for this master, when sorted for replication offset.

Usually this allows the slave with the most updated offset to win the
election and replace the failing master in the cluster.
Cluster: limit cluster.h to 80 cols.
Cluster: broadcast master/slave replication offset in bus header.
Cluster: clusterBroadcastPong() improved with target selection.

Now we can broadcast a pong to all the instances or just the local
slaves (that is useful for replication offset propagation).
Cluster: added a global myself pointer in cluster.c.

Accessing to the 'myself' node, the node representing the currently
running instance, is handy without the need to type
server.cluster->myself every time.
Cluster: use myself instead of server->cluster.myself.
Cluster: refactoring: new macros to check node flags.