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When a sentinel object from unittest.mock.sentinel is passed through a multiprocessing.Pool.map, I expect it to still be comparable. 
As a user, I'd like to be able to write a unit test using sentinels on my unparallelized code, and then see that the test still passes after I parallelize the code using multiprocessing, so that I can make use of sentinels in regression testing.
Example:
```
from unittest import mock
import multiprocessing
def identity(x):
 return x
with multiprocessing.Pool() as pool:
 multiprocessed = list(pool.map(identity, [mock.sentinel.foo]))
assert identity(mock.sentinel.foo) == mock.sentinel.foo # Passes
assert multiprocessed[0] == mock.sentinel.foo # Fails
```