The previous implementation of zmalloc.c was not able to handle out of
memory in an application-specific way. It just logged an error on
standard error, and aborted.

The result was that in the case of an actual out of memory in Redis
where malloc returned NULL (In Linux this actually happens under
specific overcommit policy settings and/or with no or little swap
configured) the error was not properly logged in the Redis log.

This commit fixes this problem, fixing issue #509.
Now the out of memory is properly reported in the Redis log and a stack
trace is generated.

The approach used is to provide a configurable out of memory handler
to zmalloc (otherwise the default one logging the event on the
standard output is used).

This bug was spotted by clang on FreeBSD.

clusterGetRandomName() generalized into getRandomHexChars() so that we can use it for the run_id field as well.

Fixed a non critical bug signaled by clang static analyzer thanks to Mukund Sivaraman for reporting it: there was a not initialized field populating the cluster message header, but it is always fixed at later time before sending the packet.

Redis Cluster: process node to node CLUSTERMSG_TYPE_PUBLISH messages and send it to the local clients.

propagate PUBLISH messages using the redis cluster nodes bus. Still need to process the incoming packets of that type. Work in progress.

A node can populate a slot if a message from a trusted slot is received claiming ownership of this slot, that is currently empty or served by a node in FAIL state. However this feature was broken since calling clusterAddSlot() was not enough as the slot bit is already set in the node that pong us. We need to directly alter the table. This commit fixes the issue.

Rewrite MIGRATE as DEL for AOF/replication. Also increment the dirty counter to both force replication and persistence.

increment server.dirty in restore command to make sure it is replicated and increments the dirty count for persistence concerns.

when processing gossip packets make sure to also update the node bitmap when associating slots to nodes. Fixed simply using the appropriate helper function to add a slot.

Clear the importing status from the slot if a CLUSTER SETSLOT command permanently assigns the slot to the importing node.

rioInitWithFile nad rioInitWithBuffer functions now take a rio structure pointer to avoid copying a structure to return value to the caller.