Process events with processEventsWhileBlocked() when blocked.

When we are blocked and a few events a processed from time to time, it
is smarter to call the event handler a few times in order to handle the
accept, read, write, close cycle of a client in a single pass, otherwise
there is too much latency added for clients to receive a reply while the
server is busy in some way (for example during the DB loading).

src/redis.h

@@ -940,6 +940,7 @@ int getClientLimitClassByName(char *name);
 char *getClientLimitClassName(int class);
 void flushSlavesOutputBuffers(void);
 void disconnectSlaves(void);
+int processEventsWhileBlocked(void);
 
 #ifdef __GNUC__
 void addReplyErrorFormat(redisClient *c, const char *fmt, ...)