We have them into zmalloc.c, but this is going to replace that
implementation, so that it's possible to use the same idea everywhere
inside the code base.

After the introduction of the list with clients with pending writes, to
process clients incrementally outside of the event loop we also need to
process the pending writes list.

May potentially improve locality... not exactly clear if this makes a
difference or not. But for sure is harmless.

The code was broken and resulted in redis-cli --pipe to, most of the
times, writing everything received in the standard input to the Redis
connection socket without ever reading back the replies, until all the
content to write was written.

This means that Redis had to accumulate all the output in the output
buffers of the client, consuming a lot of memory.

Fixed thanks to the original report of anomalies in the behavior
provided by Twitter user @fsaintjacques.

HINCRBY* tests later used the value "tmp" that was sometimes generated
by the random key generation function. The result was ovewriting what
Tcl expected to be inside Redis with another value, causing the next
HSTRLEN test to fail.

Georadius works by computing the center + neighbors squares covering all
the area of the specified position and radius. Then a distance filter is
used to remove elements which are actually outside the range.

When a huge radius is used, like 5000 km or more, adjacent neighbors may
collide and be the same, leading to the reporting of the same element
multiple times. This only happens in the edge case of huge radius but is
not ideal.

A robust but slow solution would involve qsorting the range to remove
all the duplicates. However since the collisions are only in adjacent
boxes, for the way they are ordered in the code, it is much faster to
just check if the current box is the same as the previous one processed.

This commit adds a regression test for the bug.

Fixes #2767.

Related to #2765.

getExpire() returns -1 when no expire exists.

Related to #2765.

MOVE was not able to move the TTL: when a key was moved into a different
database number, it became persistent like if PERSIST was used.

In some incredible way (I guess almost nobody uses Redis MOVE) this bug
remained unnoticed inside Redis internals for many years.
Finally Andy Grunwald discovered it and opened an issue.

This commit fixes the bug and adds a regression test.

Close #2765.

redis-sentinel crash if ckquorum command is executed without args

As Oran Agra suggested, in startBgsaveForReplication() when the BGSAVE
attempt returns an error, we scan the list of slaves in order to remove
them since there is no way to serve them currently.

However we check for the replication state BGSAVE_START, which was
modified by rdbSaveToSlaveSockets() before forking(). So when fork fails
the state of slaves remain BGSAVE_END and no cleanup is performed.

This commit fixes the problem by making rdbSaveToSlavesSockets() able to
undo the state change on fork failure.