Chunked loading of RDB to prevent redis from stalling reading very large keys.

src/redis.h

@@ -596,6 +596,7 @@ struct redisServer {
     off_t loading_total_bytes;
     off_t loading_loaded_bytes;
     time_t loading_start_time;
+    off_t loading_process_events_interval_bytes;
     /* Fast pointers to often looked up command */
     struct redisCommand *delCommand, *multiCommand, *lpushCommand, *lpopCommand,
                         *rpopCommand;