Thread based error on replicating object associated with a object spawning multiple threads

Example: 

```
con = Connection()
db = con.database("RASBASE")
col = RasCollection("rgb")
col.use_db(db)
col+=2
```

should throw an error while 

```
con = Connection()
db = con.database("RASBASE")
col = RasCollection("rgb")
col+=2
col.use_db(db)
```

shouldn't.

Possibly something going funky in the Python GIL. 
