CLIENT PAUSE may be used, in other contexts, for a long time making all
the slaves time out. Better for now to be more specific about what
should disable senidng PINGs.

An alternative to that would be to virtually refresh the slave
interactions when clients are paused, however for now I went for this
more conservative solution.

In fast systems "SLOWLOG RESET" is fast enough to don't be logged even
when the time limit is "1" sometimes. Leading to false positives such
as:

[err]: SLOWLOG - can be disabled in tests/unit/slowlog.tcl
Expected '1' to be equal to '0'

sdsTest() defined in sds.c dit not match the call in server.c.
remove it from REDIS_TEST, since test-sds defined in Makefile.

solving few replication related tests race conditions which fail on slow machines

bugfix in slave buffers test: since the test is executed twice, each time with
a different commands count, the threshold for the delta can't be a constant.

Add a flag to automatically protect filters from being called
recursively by their own module.

A filter handle is returned and can be used to unregister a filter.  In
the future it can also be used to further configure or manipulate the
filter.

Filters are now automatically unregistered when a module unloads.

in diskless replication - master was not notifing the slave that rdb transfer
terminated on error, and lets slave wait for replication timeout

Related to #3829.

See #3829.

also reduce an excess sleep

this is very confusing to see the server disappears as if it got SIGKILL when it was not the case.

Enlarge error buffer in redis-check-aof.c to remove compiler warning of output truncation through snprintf format string

Hi, @antirez

In the code, to get the size of ziplist, "unsigned int bytes = ZIPLIST_HEADER_SIZE+1;" is correct, 
but why not make it more readable and easy to understand