zrank and zscore fail with integer members

In client.py:zadd(), the member is converted to a string:

```
        insert_count = lambda member, score: 1 if zset.insert(str(member), float(score)) else 0
```

but not also done in sortedset.py:zscore() and zrank(), so if you:

```
zadd(key, 12345, 1.0)
zscore(key, 12345)
```

it fails to find the member.
