Sentinel: more sensible delay in master demote after tilt.
Sentinel: changes to tilt mode.

Tilt mode was too aggressive (not processing INFO output), this
resulted in a few problems:

1) Redirections were not followed when in tilt mode. This opened a
   window to misinform clients about the current master when a Sentinel
   was in tilt mode and a fail over happened during the time it was not
   able to update the state.

2) It was possible for a Sentinel exiting tilt mode to detect a false
   fail over start, if a slave rebooted with a wrong configuration
   about at the same time. This used to happen since in tilt mode we
   lose the information that the runid changed (reboot).

   Now instead the Sentinel in tilt mode will still remove the instance
   from the list of slaves if it changes state AND runid at the same
   time.

Both are edge conditions but the changes should overall improve the
reliability of Sentinel.
Fix AOF bug: expire could be removed from key on AOF rewrite.

There was a race condition in the AOF rewrite code that, with bad enough
timing, could cause a volatile key just about to expire to be turned
into a non-volatile key. The bug was never reported to cause actualy
issues, but was found analytically by an user in the Redis mailing list:

https://groups.google.com/forum/?fromgroups=#!topic/redis-db/Kvh2FAGK4Uk

This commit fixes issue #1079.
Reset masterauth if an empty string is configured.
CONFIG SET server.masterauth aesthetic change.

This is just to make the code exactly like the above instance used for
requirepass. No actual change nor the original code violated the Redis
coding style.
Cluster: createClusterLink() comment fixed for grammar.
Cluster: process config from PING packets as we do for PONG.

Also clusterBroadcastPing() was renamed into clusterBroadcastPong()
that's what the function is actually doing.
Cluster: PING/PONG handling redesigned.
Cluster: restore PING sent time on reconnections.
Cluster: link reconnection on delayed PONG reply.

When the PONG delay is half the cluster node timeout, the link gets
disconnected (and later automatically reconnected) in order to ensure
that it's not just a dead connection issue.

However this operation is only performed if the link is old enough, in
order to avoid to disconnect the same link again and again (and among
the other problems, never receive the PONG because of that).

Note: when the link is reconnected, the 'ping_sent' field is not updated
even if a new ping is sent using the new connection, so we can still
reliably detect a node ping timeout.
in 32bit machine, popcount don't work with a input string length up to 512 MB,
bitcount commant may return negtive integer with string length more than 256 MB
use long long instead of size_t make it more safe
Added more info about 32 bit builds into README.
Merge pull request #1093 from july2993/unstable

in 32bit machine, popcount don't work with a input string length up to 5...
Revert "use long long instead of size_t make it more safe"

This reverts commit 2c75f2cf1aa0d9cc8256517bd6f3d8a82088ee1a.

After further analysis, it is very unlikely that we'll raise the
string size limit to > 512MB, and at the same time such big strings
will be used in 32 bit systems.

Better to revert to size_t so that 32 bit processors will not be
forced to use a 64 bit counter in normal operations, that is currently
completely useless.
Test: various issues with the replication-4.tcl test fixed.

The test actually worked, but vars for master and slave were inverted
and sometimes used incorrectly.
Test: check that replication partial sync works if we break the link.

The test checks both successful syncs and unsuccessful ones by changing
the backlog size.
Version bumped to 2.9.10
Test: more PSYNC tests (backlog TTL).
Obtain absoute path of configuration file, expose it in INFO.