PFSELFTEST: less false positives.

This is just a quickfix, for the nature of the test the right way to fix
it is to average the error of N runs, since otherwise it is always
possible to get a false positive with a bad run, or to minimize too much
this possibility we may end testing with too much "large" error ranges.
Faster ll2string() implementation.

Based on ideas documented in this blog post:

https://www.facebook.com/notes/facebook-engineering/three-optimization-tips-for-c/10151361643253920

The original code was modified to handle signed integers, reformetted to
fit inside the Redis code base, and was stress-tested with a program
in order to validate the implementation against snprintf().

Redis was measured to be measurably faster from the point of view of
clients in real-world operations because of this change, since sometimes
number to string conversion is used extensively (for example every time
a GET results into an integer encoded object to be returned to the
user).
Fix util.c compilation by including stdint.h.
Cluster: don't migrate to a master that never had slaves.

Replica migration algorithm modified so that slaves never try to migrate
to masters that were never configured to have slaves in the past.
We want the algorithm to take care of masters that remained without
*working* slaves, but that used to have slaves according to the cluster
configuration.
Cluster test: new unit 05, slave selection.
Example redis.conf: improve slaveof description.
Cluster test: unit 06, slaves with stale data can't failover.
Cluster test: 03 unit speedup, don't send WAIT to slaves.
Cluster test: init test, be patient during restarts.
Cluster test: node reachability condition fixed.
Fix spelling of "stand alone" in ascii art

Also unified the logic to match `genRedisInfoString`
Merge pull request #1895 from mattrobenolt/patch-1

Fix spelling of "stand alone" in ascii art
Cluster test: unit 06 cluster creation comment fixed.
Cluster test: unit 07, replicas migration.
Merge branch 'unstable' of github.com:/antirez/redis into unstable
* fixed doc URL for keyspace events
Fail SYNC if background save child aborted due to a signal.
Merge pull request #1896 from yossigo/bgsave-signal-fix

Fail SYNC if background save child aborted due to a signal.
Remove unused global variable commandTable
Add dynamic command loading

We can now add custom commands to Redis without recompiling.

Add commands by creating a shared library containing:
    - a table exporting your command definitions
      - (exactly the same as redisCommandTable has always been)
    - a string defining the name of your module

You can add modules in redis.conf with
    "module-add [module.so]"
or on the command line with
    redis-server --module-add module.so
or at runtime with
    "CONFIG SET MODULE-ADD [module.so]"

If you add a module twice, the second time will:
  - load the new module
  - unload the previous module
  - overwrite commands from the old module with
    commands in the new module
  - reset per-command stats/counters for each of
    the newly re-added commands

(Note: Any commands in the old module but not
in the new module will stick around.  To remove a command you
should keep it in your module and just give it a
noop definition or alias it to something simple like the
ping command.)

(Note: There is no way to remove or unload
a module.  You can only add modules and reload existing
modules by re-adding them.  To remove a module, restart
Redis.)

(Note: Running a master-replica or cluster setup with Redis
instances not containing the same set of modules will break
horribly.  Either fully distribute your modules or don't
use modules with replicated Redis.)

This commit contains these changes:
    - Make sure the Redis command table ends with a NULL entry
    - Rename populateCommandTable() to populateCommand(), and
      make it only process one command per invocation.
    - Replace all numcommands calculations with redisCommands.length.
    - Replace usage of redisCommandTable with redisCommands.table.
    - Replace the server startup call to populateCommandTable()
      with a call to loadDynamicCommands(NULL).  When given NULL,
      loadDynamicCommands reads the command table from the
      redis-server executable instead of an externally loaded module.
      Yes, that means the same mechanism used to import new commands
      from external modules bootstraps built-in commands too.
    - Add new INFO MODULES section to output all loaded
      modules, with their names, library filenames, original
      load timestamp, most recent load timestamp (for when
      modules are reloaded with CONFIG SET), and the list of
      commands the module provides.  Note: The redis-server itself
      is processed as a module, so it shows up as module <builtin>.
    - Add new configuration option 'module-add'.
    - Add new CONFIG SET option 'module-add'.

Example output of INFO MODULES:
    127.0.0.1:6379> info modules
    # Modules
    module_demo_ping:filename=ping.so,first_loaded=0,last_loaded=1395789529,commands=poong,pooooong,pooong
    module_<builtin>:filename=<builtin>,first_loaded=0,last_loaded=0,commands=get,set,setnx,setex,psetex,append,strlen,del,exists,setbit,getbit,setrange,getrange,substr,incr,decr,mget,rpush,lpush,rpushx,lpushx,linsert,rpop,lpop,brpop,brpoplpush,blpop,llen,lindex,lset,lrange,ltrim,lrem,rpoplpush,sadd,srem,smove,sismember,scard,spop,srandmember,sinter,sinterstore,sunion,sunionstore,sdiff,sdiffstore,smembers,sscan,zadd,zincrby,zrem,zremrangebyscore,zremrangebyrank,zunionstore,zinterstore,zrange,zrangebyscore,zrevrangebyscore,zcount,zrevrange,zcard,zscore,zrank,zrevrank,zscan,hset,hsetnx,hget,hmset,hmget,hincrby,hincrbyfloat,hdel,hlen,hkeys,hvals,hgetall,hexists,hscan,incrby,decrby,incrbyfloat,getset,mset,msetnx,randomkey,select,move,rename,renamenx,expire,expireat,pexpire,pexpireat,keys,scan,dbsize,auth,ping,echo,save,bgsave,bgrewriteaof,shutdown,lastsave,type,multi,exec,discard,sync,psync,replconf,flushdb,flushall,sort,info,monitor,ttl,pttl,persist,slaveof,debug,config,subscribe,unsubscribe,psubscribe,punsubscribe,publish,pubsub,watch,unwatch,cluster,restore,restore-asking,migrate,asking,readonly,readwrite,dump,object,client,eval,evalsha,slowlog,script,time,bitop,bitcount,bitpos,wait

(Note: {first,last}_loaded of 0 means it was loaded at startup from a configuration
directive or command line argument.  If loaded != 0, then the module
was evaluated after the server started using CONFIG SET MODULE-ADD [module.so])