More doc fixes. Latex builds again.

doc/datasets/index.rst

doc/modules/clustering.rst

doc/whats_new.rst

examples/applications/face_recognition.py

examples/ensemble/plot_partial_dependence.py

sklearn/calibration.py

sklearn/covariance/graph_lasso_.py

sklearn/cross_validation.py

sklearn/decomposition/nmf.py

sklearn/ensemble/voting_classifier.py

sklearn/feature_selection/rfe.py

sklearn/grid_search.py

sklearn/learning_curve.py

sklearn/linear_model/coordinate_descent.py

sklearn/linear_model/least_angle.py

sklearn/linear_model/omp.py

sklearn/linear_model/ridge.py

sklearn/metrics/classification.py

sklearn/metrics/regression.py

sklearn/preprocessing/data.py