sklearn

* FIX Subclass a new MaskedArray which allows pickling even when dype=object

* TST unpickling too

* FIX Use MaskedArray from utils.fixes rather than from numpy

* FIX imports

* Don't assign a variable

* FIX np --> numpy

* Use tostring instead of tobytes for old numpy

* COSMIT pickle-able --> picklable

* use #noqa comment to turn off flake8

* TST/ENH Check if the pickled est's predict matches with the original one's