LFU: Redis object level implementation.

Implementation of LFU maxmemory policy for anything related to Redis
objects. Still no actual eviction implemented.

src/config.c

@@ -45,9 +45,11 @@ typedef struct configEnum {
 
 configEnum maxmemory_policy_enum[] = {
     {"volatile-lru", MAXMEMORY_VOLATILE_LRU},
+    {"volatile-lfu", MAXMEMORY_VOLATILE_LFU},
     {"volatile-random",MAXMEMORY_VOLATILE_RANDOM},
     {"volatile-ttl",MAXMEMORY_VOLATILE_TTL},
     {"allkeys-lru",MAXMEMORY_ALLKEYS_LRU},
+    {"allkeys-lfu",MAXMEMORY_ALLKEYS_LFU},
     {"allkeys-random",MAXMEMORY_ALLKEYS_RANDOM},
     {"noeviction",MAXMEMORY_NO_EVICTION},
     {NULL, 0}