Added code to address issue #1403
In preprocessing.binarize, eliminate zeros from sparse matrices
implement AdaBoost
use weighted mean in ClassifierMixin.score
ENH: weighted r2 score for regression
COSMITs
ENH: Added balance_weights
ENH: added some tests
FIX: test_oob_score_regression
FIX: DecisionTreeRegressor.score
FIX: compute weighted oob scores
FIX: NaN problem + Added some tests
TEST: added some more tests
EXAMPLE: simplify n_estimators and n_samples
TEST: importances
TEST: multi-output problems
ENH: WeightedClassifier/Regressor mixins
DOC
FIX: import not used
FIX: overlapping y-axis labels