Fail to unpickle namedtuple

[AmatanHead]

Hello!

The current upstream code can't handle namedtuples.

Here's an MWE:

import cloudpickle
from collections import namedtuple

X = namedtuple('X', ['a'])

cloudpickle.loads(cloudpickle.dumps(X))

Traceback:

Traceback (most recent call last):
  File "t.py", line 6, in <module>
    cloudpickle.loads(cloudpickle.dumps(X))
  File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 1388, in loads
    return Unpickler(file).load()
  File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 864, in load
    dispatch[key](self)
  File "/usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 1139, in load_reduce
    value = func(*args)
  File "/Users/amatanhead/Documents/cloudpickle/cloudpickle/cloudpickle.py", line 1043, in _rehydrate_skeleton_class
    setattr(skeleton_class, attrname, attr)
AttributeError: attribute '__dict__' of 'type' objects is not writable

[ssanderson]

Looks like this fails because __dict__ is a property on namedtuple in python 2 (namedtuple appears to work fine in python 3). Tentative fix here: #113.

[robertnishihara]

Should be fixed by #113.