Resolve #1298

* use serial.load in CIFAR10._unpickle
* remove "scripts/tutorials/grbm_smd/make_dataset.py" from pep8 whitelist
* refine serial.load for interoparability between Python 2 and 3
* remove N and np, aliases of numpy
Yes, `six.cPickle` is just an aliase of `cPickle` module in Python 2.