兼容redis 2.4 的rdb 文件.

参考:
https://github.com/antirez/redis/blob/2.4/src/redis-check-dump.c
https://github.com/antirez/redis/blob/2.6/src/redis-check-dump.c
Update README.md
Update README.md
Update README.md
Merge pull request #1 from zhenchuan/master

兼容redis 2.4 的rdb 文件.