Add key-hash-spliting function for redis.
new command:
 1. gethashval <key-string>
    get the key-string hash value
 2. hashkeys <hash-id> <patten>
    get all the keys in hash-id of patten <patten>
 3. hashkeyssize <hash-id>
    get the keys' number stored in <hash-id> bucket

Add 2 list for each hash bucket, each bucket contain keys with the same hash value, total 420000 buckets.
For each add/del operation, just modify the pointer in the list.
fix the REDIS_HASH_BUCKETS as 420000