setup.py: add dependency on Pillow library
setup.py: add dependency on Pillow library

datasets.{asirra,base} require PIL to be installed. PIL itself isn't PyPI friendly but the Pillow fork which provides an identical interface is. Add Pillow as a dependency.
bssrdf/sklearn-theano,JesseLivezey/sklearn-theano,alexchao56/sklearn-theano,kastnerkyle/sklearn-theano,eickenberg/sklearn-theano,HRZaheri/sklearn-theano,yaoli/sklearn-theano,arnabgho/sklearn-theano,sklearn-theano/sklearn-theano,alexchao56/sklearn-theano,JesseLivezey/sklearn-theano,eickenberg/sklearn-theano,arnabgho/sklearn-theano,bssrdf/sklearn-theano,kastnerkyle/sklearn-theano,yaoli/sklearn-theano,HRZaheri/sklearn-theano