Cluster: use long long for timestamps in clusterGenNodesDescription().

Ping sent and pong received fields need to be casted to long long to be
printed correctly into 32 bit systems.
Fixed clearNodeFailureIfNeeded() time type to mstime_t.

This prevented 32bit cluster instances from clearing the FAIL flag when
needed.
Cluster: use an hardcoded 60 sec timeout in redis-trib connections.

Later this should be configurable from the command line but at least now
we use something more appropriate for our use case compared to the
redis-rb default timeout.
Cluster: use proper type mstime_t for ping delay var.
Cluster: initialize todo_before_sleep flags to 0.
Cluster: check link is valid before sending UPDATE.
Cluster: set n->slaves to NULL in clusterNodeResetSlaves().

The value was otherwise undefined, so next time the node was promoted
again from slave to master, adding a slave to the list of slaves
would likely crash the server or result into undefined behavior.
Example redis.conf formatted to better show appendfilename option.
CONFIG REWRITE: don't wipe unknown options.

With this commit options not explicitly rewritten by CONFIG REWRITE are
not touched at all. These include new options that may not have support
for REWRITE, and other special cases like rename-command and include.
CONFIG REWRITE: old development comments removed.
CONFIG REWRITE: don't throw some options on config rewrite

Those options will be thrown without this patch:
  include, rename-command, min-slaves-to-write, min-slaves-max-lag,
appendfilename.
CONFIG REWRITE: no special handling or include and rename-command.

CONFIG REWRITE is now wiser and does not touch what it does not
understand inside redis.conf.
Clarify include directive behavior in example redis.conf.
Redis Cluster: delay state change when in the majority again.

As specified in the Redis Cluster specification, when a node can reach
the majority again after a period in which it was partitioend away with
the minorty of masters, wait some time before accepting queries, to
provide a reasonable amount of time for other nodes to upgrade its
configuration.

This lowers the probabilities of both a client and a master with not
updated configuration to rejoin the cluster at the same time, with a
stale master accepting writes.
Redis Cluster: handshake code refactoring + Gossip IP switch detection.

This commit makes it simple to start an handshake with a specific node
address, and uses this in order to detect a node IP change and start a
new handshake in order to fix the IP if possible.
Redis Cluster: reconfigure replication when master changes address.
Redis Cluster: remove no longer relevant comment.
Redis Cluster: move node failure reports logging from VERBOSE to NOTICE level.
Log when a slave lose the connection with its master.
Redis Cluster: add repl_ping_slave_period to slave data validity time.

When the configured node timeout is very small, the data validity time
(maximum data age for a slave to try a failover) is too little (ten
times the configured node timeout) when the replication link with the
master is mostly idle. In this case we'll receive some data from the
master only every server.repl_ping_slave_period to refresh the last
interaction with the master.

This commit adds to the max data validity time the slave ping period to
avoid this problem of slaves sensing too old data without a good reason.
However this max data validity time is likely a setting that should be
configurable by the Redis Cluster user in a way completely independent
from the node timeout.