check in ``if_matplotlib`` if $DISPLAY set
FIX and test deprecated import of spectral_embedding from cluster
TST better test-coverage in clustering module
COSMIT in cross-validation tests
FIX random state in test by @briancheung. Thanks
TST better coverage in dict learning and cross validation
TST better coverage in preprocessing module
DOC add matplotlib version requirement, rephrase
fix spectral related testing errors
COSMIT and unused lines
FIX further improve the thresholds
Merge pull request #1440 from amueller/matplotlib_requirement

MRG add matplotlib version requirement, rephrase
use subplots_adjust instead of tight_layout
use 100 instead of 800 n_estimators; looks the same but faster; ESLII uses 800
FIX discretization test have shape problem, use coo_matrix instead of LabelBinarizer
ZipFile context manager is only available in Python >= 2.7
Addressing @ogrisel's comments
ENH: Simplify the shape of (n_)classes_ for single output trees
COSMIT Mean Shift docs.
ENH: Simplify the shape of (n_)classes in forest