FIX P/R/F metrics and scorers are now for binary problems only by default

benchmarks/bench_multilabel_metrics.py

doc/datasets/twenty_newsgroups.rst

doc/modules/classes.rst

doc/modules/cross_validation.rst

doc/modules/model_evaluation.rst

doc/whats_new.rst

examples/model_selection/grid_search_digits.py

examples/text/document_classification_20newsgroups.py

sklearn/feature_selection/tests/test_rfe.py

sklearn/linear_model/tests/test_ridge.py

sklearn/linear_model/tests/test_sgd.py

sklearn/metrics/__init__.py

sklearn/metrics/classification.py

sklearn/metrics/scorer.py

sklearn/metrics/tests/test_classification.py

sklearn/metrics/tests/test_common.py

sklearn/metrics/tests/test_score_objects.py

sklearn/svm/tests/test_svm.py

sklearn/tests/test_cross_validation.py

sklearn/utils/estimator_checks.py