Cancel SHUTDOWN if initial AOF is being written

Fixes #1826 (and many other reports of the same problem)
hiredis: Update to latest version

This is hiredis f225c276be7fd0646019b51023e3f41566633dfe

This update includes all changes that diverged inside of Redis since
the last update.  This version also allows optional source address
binding for connections which we need for some Sentinel deployments.
Dummy zmalloc.h restored into deps/hiredis.
Add REDIS_BIND_ADDR access macro

We need to access (bindaddr[0] || NULL) in a few places, so centralize
access with a nice macro.
Sentinel: bind source address

Some deployments need traffic sent from a specific address.  This
change uses the same policy as Cluster where the first listed bindaddr
becomes the source address for outgoing Sentinel communication.

Fixes #1667
Use Redis updated sds.c for deps/hiredis.
Silence different signs comparison warning in sds.c.
Merge branch 'unstable' of github.com:/antirez/redis into unstable