Dill gives incorrect, invalid name to nested namedtuples in 3.7

[sjchilcote]

This (reduced from real-world code) example fails:

import collections, dill

class A:
    class B(collections.namedtuple("B", ["one", "two"])):
        pass

a = A()
aa = dill.loads(dill.dumps(a))

Dill thinks B is named A.B, which is not a valid name for a NamedTuple since it has to be a valid identifier, and Python gives ValueError: Type names and field names must be valid identifiers: 'A.B'

Adding the following makes it work again for me at least, but I don't know whether or not the name being wrong should be considered a deeper issue.

In _dill._create_namedtuple:

import collections
name = name.split('.')[-1] #add this line - removes the parent's name, 'A.B' -> 'B'
t = collections.namedtuple(name, fieldnames)