Replace magic 32 with REDIS_EVENTLOOP_FDSET_INCR
Replace magic 32 with REDIS_EVENTLOOP_FDSET_INCR

32 was the additional number of file descriptors Redis
would reserve when managing a too-low ulimit.  The
number 32 was in too many places statically, so now
we use a macro instead that looks more appropriate.

When Redis sets up the server event loop, it uses:
    server.maxclients+REDIS_EVENTLOOP_FDSET_INCR

So, when reserving file descriptors, it makes sense to
reserve at least REDIS_EVENTLOOP_FDSET_INCR FDs instead
of only 32.  Currently, REDIS_EVENTLOOP_FDSET_INCR is
set to 128 in redis.h.

Also, I replaced the static 128 in the while f < old loop
with REDIS_EVENTLOOP_FDSET_INCR as well, which results
in no change since it was already 128.

Impact: Users now need at least maxclients+128 as
their open file limit instead of maxclients+32 to obtain
actual "maxclients" number of clients.  Redis will carve
the extra REDIS_EVENTLOOP_FDSET_INCR file descriptors it
needs out of the "maxclients" range instead of failing
to start (unless the local ulimit -n is too low to accomidate
the request).

Hailei/redis,HunanTV/redis,Hailei/redis,himoca/redis,darksideofthemoo/redis-histogram,ttuna/msot-redis,maodeyi/redis_lua,slfs007/mk-redis,spearhead-ea/redis,MSOpenTech/redis,ksarch-saas/redis,himoca/redis,himoca/redis,louisliangjun/redis,slfs007/mk-redis,HunanTV/redis,ttuna/msot-redis,xuzhezhaozhao/redis_reading,ksarch-saas/redis,Hailei/redis,xuzhezhaozhao/redis_reading,spearhead-ea/redis,MSOpenTech/redis,MSOpenTech/redis,maodeyi/redis_lua,ramonsnir/redis,splitice/redis,louisliangjun/redis,ksarch-saas/redis,MSOpenTech/redis,darksideofthemoo/redis-histogram,jxwr/redis,MSOpenTech/redis,spearhead-ea/redis,louisliangjun/redis,ramonsnir/redis,ramonsnir/redis,splitice/redis,HunanTV/redis,ksarch-saas/redis,splitice/redis,ttuna/msot-redis,darksideofthemoo/redis-histogram,maodeyi/redis_lua,xuzhezhaozhao/redis_reading,Hailei/redis,ttuna/msot-redis,ttuna/msot-redis,HunanTV/redis,darksideofthemoo/redis-histogram,xuzhezhaozhao/redis_reading,splitice/redis,jxwr/redis,louisliangjun/redis,slfs007/mk-redis,jxwr/redis