ZODB expect userid and description to be bytes

ZODB expect user and description to be bytes.

as in ZODB/FileStorage/format.py
```python
def asString(self):
        s = struct.pack(TRANS_HDR, self.tid, self.tlen, as_bytes(self.status),
                        self.ulen, self.dlen, self.elen)
        return b"".join(map(as_bytes, [s, self.user, self.descr, self.ext]))
```

Chinese username or pathinfo will throw an exception here.