AdaBoost: use estimator weights in predict_proba
TST + DOC AdaBoostClassifier.predict_proba fix
COSMIT refactor AdaBoost code
DOC fetch_20newsgroups returns the text, not text files. see SO question: http://stackoverflow.com/questions/16615523/using-scikits-kmeans-to-cluster-ones-own-documents
DOC Fixed documentation of kernel parameters: sigm uses gamma, but not degree. Closes #1972.