Cannot ignore locks with cloudpickle

I have an object that I would like to pickle. Unfortunately, the object has a lock within it.

Is there a way to set up cloudpickle to ignore locks so that it doesn't crash?

```python
import threading
import cloudpickle

class ThirdPartyClass:
def __init__(self):
self.internal_lock = threading.RLock()
self.something_I_want_pickled = 'important string'

cloudpickle.dumps(ThirdPartyClass())

```

See also #81